I really don't think that's the reason. Not only does Apple not actually make very much revenue from iTunes, it is probably more to do with audio hardware on an iphone being limited.
Fair enough, nevertheless the motivation just doesn't ring true to me. Apple doesn't cripple things to protect revenue streams. They cripple things to maintain control.
Really? I guess 6% of it's net sales isn't a huge amount i guess, but when that equates to £6.3 billion I wouldn't regard that as small fish.