GT5 is a video game, it's hardly a simulator. I personally think it's timezone differences right now, give it a day or two. But I agree that Europeans and Asians are better drivers than US drivers but for a different reason than you.
I would say Americans are actually less limited than Europeans and Asians simply because there is more land here. We have states bigger than some European nations, we treansport food, consumeables, commodities etc across these great expanses of land. We have long, wide straight roads because the land is condusive to it, and our cars are bigger ride smoother and less stiff than Euro/Asian cars simply because we don't need them stiff and they're more comfortable to ride in loose. It has everything to do with the landmass this nation is on and how we Americans drivers interact with it and very little to do with inate skill. We have different needs than Euros/Asians and our driving style/ability reflects that.