Of course, if it's possible to learn how to learn--that is, if you can learn more efficient study methods--one would expect to see this disparity (effort expended per unit of knowledge acquired [not that you could measure this]) even in a hypothetical population of genetic clones raised in different environments.
As to why downplaying genetic potential could be a good thing, I've got this excellent pg quote fairly well seared into my brain:
"I'm not saying there's no such thing as genius. But if you're trying to choose between two theories and one gives you an excuse for being lazy, the other one is probably right." - http://www.paulgraham.com/hs.html