Well, in the real swamps of academy and governmental research (I know little about industry) scientific excellence is not (unfortunately) the only way to full blown financial/career success. Office politics, salemanship skills, hype skills, ass kissing skills, light fraud skills, etc., etc., etc are very important. That's why I am not sure about "the best stay" part. "The best" in what? If a guy is the best $grant$ getter, he'll stay employed no matter how worthless is his research/results are (money do not smell). If scientific journals will stop publishing worthless, redundant piles of "scientific" publications (necessary for survival, publish crap or perish and near worthless otherwise) I'll buy "the best stay". Secondly, deliberate overproduction of Ph.D.s (to use as cheap labor and throw out) is incredible waste of human lives.