(This is talking about math ability, not IQ per se.)
Then that would explain why we seem to be talking past each other, because I was quite clearly talking about IQ all along.
No it wouldn't explain anything. That was just a paranthetical comment to refer to the appropriate measure of ability. In almost any endeavour, achievement comes from a combination of ability and effort, and while effort can make up some ground, there is a limit to that.
You made this comment.
I would expect that PG/EG participants in math competitions find themselves up against other PG/EG participants in short order, at which point the number hours of study and practice become a significant determining factor in success. Once "Who wants it more?" is a major part of the activity, it becomes very easy for someone to say, "Not me," or, "Eh... I want it, but not that badly."
This essentially implies that people in the top 0.1% (i.e. at least +3SD above average) are all essentially at the same level of ability (and for this argument, "ability in what?" doesn't really matter). They're not at the same level of ability at all. There is as much difference between +6SD and +3SD as there is between +3SD and +0SD (average). While effort will certainly make a difference, it can't make up for huge differences in ability, for many types of endeavours.
