The really interesting thing is that you see results from all over the world showing this. Catholics in Northern Ireland in the 1970s measuring 15 points lower than Protestants. Burakumin in Japan measuring 15 points lower than non-Burakumin. SAME GENE POOL. This strongly suggests you get at least 15 points really easily just from social factors, and these studies may (because a study isn't solid science yet, not even a string of studies from the same group) point to one reason.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.