Unfortunately openness probably won't matter in the short term. If it works, and untethers iOS devices from Macs then people will use it. There is hope, however, that open wins in the long term, and Apple will eventually have to play along.
They have a pretty big trojan horse to push cloud services. iOS.
Isn't ITMS the largest distributor of digital music in the world, and 3rd or so large of music generally? I can imagine if they let you stream your music/video purchases from the cloud that they'd end up with a few customers for that.