I'm willing to bet a large part of it is that essentially, Samsung lets the carriers talk them into each getting their own custom build of the phone. Both Sprin

I'm willing to bet a large part of it is that essentially, Samsung lets the carriers talk them into each getting their own custom build of the phone. Both Sprint and T-Mobile US are getting a variant with a 4.5" screen, and there's rumbling that the T-Mobile variant is using a Snapdragon instead of Exynos to take full advantage of T-Mobile's DC-HSPA+ network. And for some reason, Samsung insists on using a different button layout on their US models (flat home/menu/back/search in US vs. menu/raised home/back on the Euro model).