That's odd. I wonder why Apple produced a phone simply for T-Mobile, Verizon, and Sprint (and the rest of the world except China) rather than just give all the US carriers the "AT&T" version? If AT&T wanted Band 30 to be exclusive to "their" phone then the other carriers wouldn't have it.
My guess is that AT&T wanted that band exclusive to them. They probably saw a whole bunch of people buy the TMO & Verizon versions last year to use on their network. I can't imagine Apple deciding to make a whole separate phone just because when they can just as easily have all bands in 1 device. Stuff like this is why I hate them (AT&T).