Even without US carriers in the middle, realize that the US versions use different hardware. That ALONE means that Samsung has it as second class treatment and that different devs are working on it, etc. Your main model always gets first class treatment.
Why else do you think I've been speaking out so much about fragmented hardware? It's great that Samsung has gotten away from totally different external hardware for the US versions, but the next step is to see if we can have a unified LTE chipset.