It could be arrogance, it could be patience.
One thing is certain: the xbox brand is still strong in the USA. Sony are aware of that and I'm certain will not justify losing marketshare due to their success worldwide.
Sony care about the US market, the proof is how much they are doing to counter the XB in it. The first signs were on the PS3, with commanding ND to grimmify their new Uncharted IP at the time, and then the release of more grim games on the whole, more FPS', and whatnot.
So yes, Sony does care about the USA, but I think that them not following MS with the pricecut is more patience than arrogance at this point. If the scales start to get close to tipping, you can be certain Sony will take measures. The US, again, is very important to them.