If your music is in iTunes, it's absolutely trivial to move it to another platform. I load my Android phone up from iTunes by dragging tracks from a playlist to a flash card, and sticking that card in my phone. If your music is in Google's cloud, now, you're hosed. Half my Google Play music I can ONLY play by streaming it to an Android device.

And @franckhertz is right on about what Apple's intransigence over DRM did for all of us. If they'd gone along with Plays For Sure, or licensed FairPlay, there'd have been no incentive for the labels to drop DRM. Amazon would just have licensed both "standards", and we'd be bitching and moaning about how we had to buy the White Album again for Zune.