7 out of 9 invitations that I've seen on here have been internationals, the other two I'm not sure of their nationalities, but they do seem to have American connections (one living in NYC and the other is a Stanford alumnus). Perhaps the sample is too small to say definitively that there is a trend, but I think you need to back off those who are suggesting there is one. Lots of other factors could be at work here (yeah, yeah... don't confuse patterns with causation), but when it comes to the speculation on these boards, I think this at least has some data to suggest it may be the case.
Oh, and congratulations, Esom!