So...how else do you plan on building an 'open' collection? Aren't you still tied to Google Play or Amazon (not following how you can't use Amazon content on Android AND iOS btw, that makes no sense at all. Amazon is Amazon). You're just choosing where you want to lock yourself into.
Yeah look its not completely open. But it is a lot more open. With amazon, I can put my music onto a sony MP3 player or an Android device. Amazon doesnt care.
iTunes does - its Apple or nothing.