I've never actually joined a community for typing, but the 2/4/5/9 thing makes sense.

My own experience offline is a bit odd, as my friend who was just as interested in typing as I was is actually an 8. And I seem to know a lot of 6s personally which is kind of funny. But they're almost all INxxs so despite the differences, we seemed to connect on that level. :) Most of them... not as interested in typing, though, really just the one 8 friend (and online there is more the usual set).