Instinctively, I think a lot of people react to threads like these, because it's easy to perceive the observation as being racist or nationalistic, even though it was not intended as such at all, and even though there was nothing in the OP to suggest that kind of view at all. It seems to activate some kind of primal monkey response, because it feels like someone is saying the American tribe (to use the terminology of widely acclaimed socialanthropologist Joe Rogan) is superior to every other tribe in the world, because they have superior fighter genes.
For this reason, you get a lot of strange responses.
"Yeah, so what, the UFC is American"
"Yeah, so what, MMA started in America!"
etc
But I think it's fairly clear to anyone that American fighters aren't better by virtue of having been born in America or having American ancestors. The biggest common denominator is probably just wrestling. The US has done a great job of organizing that sport, letting young kids pursue wrestling as a path to a good education. Back in the day, the road stopped after amateur level, but now that the UFC is here, there's a clear path from toddler level to a professional career. Completely different from most other countries in the world, where high level martial arts is, at best, a hobby for the privileged and exceptionally dedicated.
I'm not a big fan of Putin, but I'm real happy he's a martial artist. We need another cold war to set up some amazing MMA rivalry between Russia and the US. It would be worth the risk of nuclear holocaust just to see how far MMA would evolve in such conditions.
Oops, I've gone off on a tangent.