I agree that there is no way that this board is 90% atheist. That would put us on par with the membership of The National Academy of Sciences. Great company to be in, if it were true.
I think that what others have said is true, that we have a higher percentage of atheists because we were forced to critically examine all religion, including and especially our own. We eventually realized how people are fooled. It is the same reason so many of the great skeptics that don't believe in supernatural forces were and are magicians. Harry Houdini, James Randi, Penn & Teller, Michael Shermer. All great skeptics, all with a background in magic. When you've seen how the box is built, you stop believing the woman was really cut in half.