I don't think that they are the top 16 fighters in the UK, I just think the talent pool is a lot deeper in the UK than most Americans thought so they are shocked.
Don't forget that the US is 9 series into TUF whereas apart from Bisping and Pointon we haven't had any representation before. So the UK team are all desperate to embrace the concept and work as hard as possible for the opportunity whereas the US team have seen knobheads like Junie get beaten and still get fights on UFC cards.
Dana won't fly a clown in from the UK when he has a choice in the US already, so the UK guys know to get invited back you need to win or be VERY impressive in losing.
Bisping slipped just before Hendo landed a "lucky" punch.*
*sarcasm is an international language :P