To a point, yes, but there's no desperate shortage of smart amongst their existing intake, and especially once you've taken into account the career boost these institutions offer, I'm sure their alumni will do just fine even if they don't include the latent geniuses in village schools a couple of thousand miles away (many boringly white and not poor enough to make an interesting rags-to-riches story anyway). If you want prestige, it's a lot easier just to mop up the sports superstars, famous families and academic prizewinners anyway.