Though it would potentially apply to legally downloaded music or movies too.
When I buy a Dead-Tree book (from here referred to as a DT book), I can read it, my husband can read it, and if I’m so inclined I can hand it off to a friend to read cause they didn’t have the money for the hardcover and are having to wait for the paperback. Its mine.
When I buy a DT book I can store it on my bookshelves, or in a box, or in a storage facility, and, baring bad luck, I can pull it back out again 2, 3, 8, 20 years later and still read it. Its mine.
When I buy a DT book it doesn’t matter where I buy it, whether its the bookstore down the road, a major online retailer, a special order from an out of country online retailer, or from the little bookstore in France while I’m traveling. Its mine.
When I buy a DT book I’m not subject to the whims of the company I bought the ebook from. Amazon has been known to delete both individual books AND whole libraries when they feel someone might have broken the rules. Barnes and Noble requires you to keep a valid credit card on file in order to re-download books.
When I buy a DT book I’m not subject to the technology used to read it. If I buy an ebook to read on the Kindle software, and two years from now I have to buy a new reading device, I still have to download the Kindle software in order to re-read the book. Yes Kindle software is currently availible for pretty much every operating system. Are you willing to bet your entire library on the assumption that it always will be? 20 years from now?
I do buy ebooks. And currently I read them on my iPad. And the first thing I do after buying them? I strip the DRM. The second thing I do is backup the stripped file to a backup that’s not connected to the internet. Its my book, and I’m damn well going to make sure I can still access it in the future, regardless of what happens to the company I bought it from or the device I read it on.