I can lend physical books to friends, I can sell them when I'm done with them, I can buy them cheap from others who are done with them. That's freedom. And that's what the books I have the opportunity to buy on my Kindle lack (ability to lend some Kindle books in a lame way aside).
No matter how many more books I have on the Kindle because ebooks are cheaper, the only freedom I have with them are to read them on devices that Amazon decides to support and to lend my whole Kindle to someone to let them read something.