Religionists and atheists should note that this does not mean there are more intelligent atheists than religionists. The bulk of of religionists merely pull the curve back to an average. Even a random sampling of the same number of participants in each group would still result in a greater likely hood of pulling from the center of the curve of the larger group. Now with that said most people come to atheism by questioning things.. I have no problem with seeing the curve leaning forward on the atheist side.
I would like a study comparinging those who consider themselves spiritual but not religious with atheist. That would be interesting. Most people that are very solid in their spiritual but none religious beliefs went through an atheism phase.