Demographics of Atheism and Theism

Apparently the blog that this refers back to has been generating a good bit of comment. Here's why (Oh, it's at this page Religion and learning: what we know | Nick Spencer | Comment is free | guardian.co.uk):

"In short, the data seem to be showing two things. First, atheism has historically been a minority movement of better educated and higher-social grade individuals whereas theism has more affinity with the lower and lower-middle class and the less well educated. Second, this is changing, with new theists coming from a higher social grade and being better educated than new atheists."

And it's data in search of a good explanatory theory or narrative, so now's your chance; I'm still puzzling, but I'm interested in any theories or stories to explain it.