Interesting survey, and from a reputable source, Pew Research, click through. Atheists performed best in the religious knowledge survey. I think if you are raised believing something, you never investigate it and that can be a reason why atheists know more academically about many religions than their adherents do. I know that I research the things I don't believe in far more extensively than I do the things I do believe in, mainly because I don't want to make faulty assumptions.