Torah: While there is no actual proof, most people believe the result of this study is due to hundreds of years of intense intellectual development. While plumbing can definitely help Sephardim in many areas, I am not sure it will close the gap.
As far as Yeshiva students go. Another study has shown the average verbal IQ of ashkenazic yeshiva students is over 125, about 30 points higher than average. This is even higher than their secular counterparts.
Yehuda: Yes I do. There are many forms of IQ tests and as a whole they provide the best measure of intelligence.