I, too, went with you up until the subscription part. Apple is now in a good position for negotiations about that and it might bring a lot of added value to Apple TV. And the owning versus hiring thing is different for video, compared to music.
You lost me though when you started talking about phones *currently* taking over iPod functions in consumer's lives. I don't see that happening anywhere at this moment to people who own an iPod.
My take is that he reason is iTunes. iTunes makes the smallest personal device with the fewest buttons more managable than what the competition makes, and is very versatile. The only thing lacking, actually, is video subscription...
I can imagine Apple dropping GSM some time, but when they do that, it won't seem revolutionary anymore. Apple is an early adopter of standards, not a leader.
I suppose the MVNO is an option Apple keeps considering, just in case, but as long as at&t serves them well (and they will, it seems), I don't think that will happen.
G