IQ tests are based on logic, not intelligence. I know a dyslexic lad (a rare form of it giving you incredible logic, but terrible maths and literacy skills) who scores literally genius level in those tests, but you talk to him and he's just a normal guy. I'm supposed to be pretty damn intelligent and I score less than him

(then again I listen to Behemoth, so ignore that).
My point is that gamers will naturally have developed a greater sense of logic from repeatedly doing lots of little puzzles within games. Even something as minimal as using a control pad confuses the hell out of some people. Essentially, as a gaming community, this place attracts those with a great logic, and therefore IQ.
Having a high IQ doesn't make you a genius, that's just a myth. What's more, people who are going to post their IQ aren't going to be people with an IQ of 90... I mean who's gonna admit that? :S