I keep seeing this parroted, and while it may have some truth to it, it seems to just be a cover story for racial quotas.
Said another way, I think that a white, a black, and an Asian raised in the valley probably have a much less diverse cultural background than say, three whites from SF, Mississippi, and NYC.
But in that instance people would just complain it is too white and needs 'culture.'
I'm OK with the culture argument, as long as you don't just throw it behind racial lines, which does a huge disservice to everyone and makes a lot of not so nice assumptions.