Or Satoshi is an American (or at least wants his wealth in USD)
On a more serious note; I think bitcoin is slightly less unknown in the US than elsewhere. AFAIK, its not like its had massive media coverage in the US, but at least some. Where I live in the EU, I have yet to see any mainstream media attention whatsoever. I have yet to meet anyone thats heard of it. The result of that could be that most miners now are US, or most of the speculators that fueled the $30 bubble. But its only a matter of time before the Chinese take over