I wonder if language plays a big part in the results, too... there are probably loads of Italian Aspies, but they're over on an Italian language Aspie forum somewhere.  Ditto the Middle Eastern Aspies and the Asian Aspies.

Then, there'll be populations - southeast Asian and Indigenous Australian, for argument's sake - who are more likely to have socioeconomic barriers to both getting internet access to take part in fora like these, and getting diagnosed in the first place.