You don’t buy Windows, you rent it. You get to keep it so long as you don’t make significant changes to your computer. They’re watching your computer, and alterations can end up cutting your system off.
If intellectual property were really property, the metaphor would cut both ways. The fact that it doesn't, that you don't have the rights one would expect when you buy intellectual property in a box at a place like CompUSA or OfficeDepot, that you would when you buy a copier or a fax machine, is more reason to abandon that damaging metaphor that has shaped our laws.