Sorry to derail your thread, but this is an appropriate arena to say this: it is completely ridiculous to think of things as "religious" vs. "atheist." Atheism is a distinctly fringe subset of being "non-religious," and the vast majority of people who do not have a religion are NOT atheists. Even among millennials, where organized religion is facing a decline, atheists remains a tiny minority.
Anyway, as SG said, economic issues often rule the day. According to Gallup, Democrats making less than $30,000 annually are actually PRO-LIFE by about a 5% margin. I doubt they go to the voting booth thinking about Roe v. Wade if they're seeing ads every week talking about how Mitt Romney outsourced jobs and wants tax cuts for millionaires.
http://www.gallup.com/poll/147941/republicans-unified-democrats-abortion.aspx