I just noticed a big difference in the user structure of Serverfault and this site (the two I use). Having a look at the first page (36 people) of the most active users this year this turns out:
Serverfault (Top 10)
USA : 22 (9)
abroad: 13 (1)
unknown : 1 (0)
Linux & Unix (Top 10)
USA : 9 (3)
abroad: 18 (6)
unknown : 9 (1)
Of course, that's nothing you have to think about. But one may find that interesting. You could guess that the importance of Linux & Unix is much higher outside the US than within. Or that the foreigners have good (compared to SF) local forums for professional IT but rather bad local forums for Linux & Unix... ;-)