As I understand it, the primary reason Lightning was chosen over micro USB was simply that the iPad needs more power than micro USB is specified to provide.

I don't think that's the case. First, they were coming off the older 30-pin dock connector. Second, the connector needs to do far more than just syncing and charging. It's also used for video out, audio out, sensor input, and who knows what other future updates. Apple designed Lightning to be very flexible for future use.

Honestly I don't believe that if USB 3 was more common Apple would have gone with it.