When Samsung announced the Galaxy S III earlier today, they didn't mention much about the US release. What we do know is that it will be coming in June, and bearing LTE technology for US networks. However, an easily overlooked detail is that Samsung's press release says that "specifications may differ on the LTE version."
This has been the case before, for example the T-Mobile Galaxy S II has a Quallcomm processor at a slightly higher clock speed than the Samsung Exynos found in other Galaxy S II variants. As T-Mobile is currently the only US carrier who has yet to roll out a LTE network, it looks like they will also be the odd one out with the Galaxy S III. This time, thought, the distinction may be seen by many as a good thing.
It has been speculated that the LTE version of the S III will require Samsung to use a different SOC (system on a chip) with support for LTE, but which will only be compatible with a dual-core processor. If true, then this would mean that T-Mobile would be the only US carrier to get the Galaxy S III with Samsung's Exynos 4 Quad, and the other carriers might get dual-core Snapdragons.
That's not to say that Snapdragons are bad, in fact the dual-core S4 is an amazing processor and used in some of the HTC One phones. Still, it might make a difference to some buyers that they don't have the quad-core spec, and some users may actually plan on utilizing those cores in some way. For most users, it probably won't matter, but if you do want the quad-core Galaxy S III in the US, there's always T-Mobile's insanely cheap unlocked plans.[Android and Me]