I think the assumption here was that, since what we were talking about was the average intelligence of the (voting) population (however fuzzy, silly or unprovable a notion), there is most likely no extremity of the kind you're talking about - for example the kind you'd find in the income curve - that would pull the average away from the median on that kind of scale.
I mean, what you're saying is that there is no
statistical reason why the majority should be near the average or why there shouldn't be an overwhelming majority clearly above or underneath the average - its all about how much of extremities are involved. And when you mention the income curve, thats a clear example. But the talk (for better or for worse) was about your potential voter population's average intelligence - and its just kind of hard to see how anything similar would come up there. I mean, unlike with income, when you can earn 100 or 10,000 times as much as someone else, can you really be 10,000 times as intelligent as someone else?
Oy, now we're asking philosophical questions ...