Amazon freely convert epub stuff so I can buy epub books (assuming DRM free) and read them from my kindle should I so choose. It's much less convenient as I have to buy then from many different companies and have to make my own back up of said books.

Fortunately, I can rip the DRM off things I buy trivially so if I move away from kindle I can take my books with me if I don't mind a little bit of law breaking (in the same way that ripping my CDs to mp3 and listening to them on my mp3 player is illegal).