Funny that he doesn't cite the studies. Besides religious people is kinda louded. What religious people? What religions? Were there difference in intelligence and degrees of religiosity? Would this hypothesis work for those who are spiritual but not religious... lol
edit: Let me add to this that mediating variables may influence the results. Poorer people tend to be more religious. So perhaps Atheist thinks Religion--Less Intelligence... Where maybe Religious--Lower Economic Status--Intelligence. Cross sectional studies (in the social sciences) are useful; however, one must know that they can't prove causal relations. So it would be interesting to get hold of the raw data and run it through SPSS to infer further about potential mediating variables, if the studies measured for specific demographic variables.