I disagree with your premise, which makes the error pointed out in above posts -- accepting the idea of "intellectual property" as though it were analogous to physical property.

But the reality is that there is no such thing as "owning" a copyrightable work of expression like Bob Dylan's lyrics. Instead, some people have temporary legal control over who may copy those lyrics and for what purpose. There is no moral or legal sense in which someone else "owns" those words on the page in front of me and I am not in any way "leasing" or "borrowing" the words. However, they may still try to restrict what I can do with those words.

So DRM is about technologically limiting others' rights, usually in some way above and beyond legal limitations. For example, if you buy a DVD, you legally have the right to make copies for personal use, or e.g. use 30 seconds of footage in your own work of art. But DRM may prevent you from exercising those rights.

However, I completely agree that it is misleading of companies to use the word "buy" when what you're acquiring remains under their control, not yours.