Music recordings: 26.7% per year
Television shows: 16.8%
Miscellaneous: 10.9% (e.g. "theatrical play scripts, stock photography, greeting-card designs, etc.).
On a straight line depreciation basis, this would give a movie a useful life of 26 years, miscellaneous cultural properties about 9 nine years, books about 8 years, television shows about 6 years, and music recording about 4 years. A percentage reduction each year would never get quite to zero and would also reach say 1% or less, considerably more slowly. The post at Slate by by Matthew Yglesias doesn't source his figures, so its hard to tell.
These numbers seem quite low to me (i.e. my intuitive estimate of the rate at which cultural investments depreciate would be higher), but all of these numbers make two points very clear.
First: Existing copyright law protection time periods grossly exceed the typical time period in which the vast majority of the economic value of an intellectual property asset is realized, even if you look at entire asset classes which weight the time period of economic returns heavily towards the rare mega-successful works with longer shelf lives.
Second: Different kinds of cultural properties protected by copyrights actually have very different useful economic lives.
As an aside, it is interesting to note that website IIMDb.com is so credible that it is used to help calculate our nation's GDP.
UPDATE: The source for the article appears to be here:
Capitalization of entertainment, literary, and other artistic originals Some entertainment, literary, and other artistic originals are designed to generate mass reproductions for sale to the general public and to have a useful lifespan of more than one year. For 1929 forward, BEA will capitalize these items, which include theatrical movies, long-lived television programs, books, music, and “other” miscellaneous entertainment. This change will expand BEA’s measures of intangible assets in the NIPAs and help better align the NIPAs with recommendations of the SNA.
Current treatment The costs associated with the production of entertainment originals are currently classified as expenses that are consumed as part of the production of other goods and services. Therefore, expenditures for the production of entertainment originals do not enter into the calculation of GDP.
New treatment Under the new treatment, BEA will record the private expenditures associated with producing or purchasing entertainment originals as private fixed investment in the measure of GDP. The production of entertainment originals may span several years. Theoretically, these costs should be recorded as investment when accrued; however, due to practical constraints, BEA will record the value of the investment in the year the asset is released to the public. Entertainment originals are rarely sold in an open market, so it is difficult to observe market prices for these original works. This is a common problem with measuring the value of intangible assets, and in such cases, other valuation methods must be utilized, such as the sum of the production costs (which is used for own-account software and R&D) or the estimated net present value (NPV). Because adequate information on production costs is not available for most entertainment originals, BEA will estimate the value of these assets based on the NPV of expected future royalties or other revenue obtained from these assets, net of any associated sales costs. For investment in theatrical movies prior to 2007, the estimates will be derived using a production costs approach based on movie budget data. For each type of entertainment originals asset, the expected net cash flow of the producing industry will be estimated using revenue and cost data from the Census Bureau’s economic censuses and surveys, numerous trade sources, and databases such as IMDb.com. BEA will assume a 7 percent real discount rate for all asset types and will apply an NPV adjustment factor, a ratio that represents the average NPV-to-current period revenues from new works, to current-year revenues in order to derive an estimate of investment in entertainment originals for that year.
Estimation methodology. First, total current-period revenue from licensing fees, merchandise sales, ticket sales, and other revenue generating activities for the industries producing the assets will be estimated. Second, the value of sales costs—such as advertising, manufacturing of reproductions, and other marketing type costs—will be subtracted from the total current period revenues to derive net revenue values that capture only the revenues earned on the intangible assets held by the business. Third, these net revenue values will be adjusted further to only include the revenue from the release of new works (that is, the “originals”), using BEA-derived investment ratios.26 Finally, the NPV adjustment factor will be applied to the net revenue value that has been adjusted by the investment ratio in order to derive the current-period investment value of the future revenue stream of these new works.
Depreciation of newly recognized assets. The depreciation of entertainment originals assets, like the depreciation of R&D assets, will be included in the NIPA measure of CFC. BEA will estimate service lives and depreciation rates for each type of entertainment originals asset based on its net present value over time as described above. The depreciation rates will follow a geometric pattern in which a constant percentage of the existing asset stock depreciates each year. The typical movie, for example, is released in theaters, followed by DVDs, premium television, regular cable networks, foreign television, and U.S. broadcast networks. Based on an analysis of the profits obtained from these successive releases, BEA estimates an annual depreciation rate of 3.8 percent. For television programs, which earn a substantial proportion of their long-term revenue in their first airing, the depreciation rate is 16.8 percent. For music, an even larger portion of profits is obtained in the first year of release, and so the estimated depreciation rate is 26.7 percent. The estimated depreciation rate is 12.1 percent for books and 10.9 percent for theatrical play scripts, greeting card designs, and stock photography.  Long-lived television programs include situation comedies and drama programs. Other types of television programs, including news programs, sporting events, game shows, soap operas, and reality programming have much shorter service lives and will not be capitalized. “Other” miscellaneous entertainment includes miscellaneous artwork including theatrical play scripts, greeting card designs, and commercial stock photography. . . .
The recognition of entertainment originals as investment will boost the level of gross private domestic investment, which will in turn boost the level of GDP. Based on preliminary research, private investment in entertainment originals for 2007 is estimated at about $70 billion. About one-third of the new investment is in theatrical movies, one-third in television programs, and the remaining one-third in the other entertainment original assets."
22. This change was introduced in a SURVEY article by Rachel H. Soloveichik, “Artistic Originals as Capital Assets,” SURVEY 91 (June 2011): 43–51. See also SNA 2008, 207, paragraph 10.115 and “Entertainment, Literary, and Artistic Originals,” in the Handbook on Deriving Capital Measures of Intellectual Property Products (Organization for Economic Cooperation and Development (OECD): Paris, October 2010): 150–166.
23. BEA will not identify any investment in entertainment originals by governments.
24. The SNA discusses the use of NPV for estimating the value of assets (SNA 2008, 22, paragraph 2.60, 52, paragraph 3.137–138); see also the OECD Handbook on Deriving Capital Measures of Intellectual Property Product, 18, 158–159.
25. BEA will benchmark its investment estimates to revenue data from the 2007 economic census.
26. Based on research using trade sources, studies, and survey and economic census data from the Census Bureau, BEA estimates the following investment ratios for the five categories of entertainment originals assets: 51 percent of industry revenue for theatrical movies, 50 percent of industry revenue for music, 37 percent of industry revenue for books, 30 percent of industry revenue for television, and 15 percent of industry revenue for miscellaneous artwork. The remaining revenue is spent on nonartwork costs such as advertising, stamping DVDs, or printing books. The NIPAs record these nonartwork costs as current production costs.The key June 2011 paper that developed these estimates is here. It notes that:
Before 2005, IMDB.com data—which gives filming dates and production budgets for individual movies from 1900 to 2011—were used to estimate annual investment expenditures. . . .
Theatrical movies and television programs have the longest lifespans. Ten years after the first release, theatrical movies retain 48 percent of their initial value, and television programs retain 35 percent of their initial value. In contrast, books and music earn most of their money in the first 5 years; after 10 years, music retains 19 percent of its initial value, and books retain 14 percent of their initial value.
The main reason for the different lifespans among the categories is consumer storage. Theatrical movies and television shows get most of their money from television licensing. Accordingly, the studios get paid each time a classic movie or television episode is replayed. In contrast, books and music get most of their money from the initial sale. Once consumers have bought a book, they can reread it without paying more money to the publisher. In this paper, only the capital stock of original artwork was measured. Therefore, the reprint rights owned by publishing houses are counted but not the physical books owned by libraries and consumers. The depreciation schedules in chart 4 are based on revenue net of sales costs. Studios, musicians, and authors typically spend a great deal of money advertising their new releases. BEA’s general practice is to treat advertising as a current expense. Because advertising is a current expense, all advertising costs are deducted from revenue for a particular year. As a result, first year profits are much lower than first year revenue. In fact, theatrical movies actually have losses in the first quarter and therefore appear to gain value early in their lifespan. Some might consider advertising a long-lived investment in brand awareness. That treatment of advertising suggests higher depreciation rates for artwork in the first year after release.
9. IMDB reports data for most major movies, with better coverage of recent movies and more expensive productions. The missing data were imputed.
19. The depreciation rate for television programs is still preliminary and may change significantly in the final version.
20. Consumers can tape a movie or television program when it is first aired and then watch it whenever they chose. In practice, very few people use their DVR for long-term storage. Instead, they watch whatever is on.
21. However, the capital value of artwork plus capitalized advertising would be identical to my capital values for artwork alone.