I was under the impression that the main reason you end up with a range of different models to deal with LTE was technical/regulatory rather than any nonsense from the carriers.

I thought it was down to the fact that supporting a wide range of frequencies without adding lots of extra antennas and power amplifiers was still problematic ?

(this is different from the silliness you get on the Android side where a single model of phone ends up with completely different CPUs and other hardware in different parts of the world or just on different carriers)