I don't know what to add except that I agree largely with Atmosfear's position vs. Sole's position.
I'll also add that, again in accordance with Gladwell's ideas, environment and "the times" play as great a role as anything else. Do you honestly think that a person who is genetically the same as Bach and had experienced similar hardships as well as a similar immersion in music would also become as great and recognized a composer today as he was at the turn of the 18th century? Of course not; Bach was Bach not only because of who he was "intrinsically" (if you can even consider a person's intrinsic qualities, which is dubious), but also because of where and when he was as well as the incidences of his life outside of himself or his control.
Again, as Atmosfear already said, we're not talking the top quintile of intelligence as "smart enough"; we're talking more like the top 45-35% of the population as being "smart enough." You have to be merely bright to get to the very top, not a genius; what most people studying this sort of stuff say is that having the intelligence of the average college educated person is completely sufficient.
As for why everyone isn't on Forbe's Wealthiest list, the simple unadorned answer is because there is very little room at the top...
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