There are many many very smart white/black/asian people. There are many many very stupid white/black/asian people.
Even if the whole cranium thing is true, it's a useless statistic. It isn't remotely reliable in predicting the intelligence of the next white/black/asian person you'll meet, so what's it worth? Like someone said, there's typically more genetic variety between random individuals than there is between races as a whole. So how is race useful?
I'm not even being PC here... this is just simple practicality.