There's an ungoing debate in the G&O forum about IQ and intelligence and in which way they correlate.
IQ is a very strictly defined construct of intelligence, IQ is culturally biased and varies over time. It's useful as indicator but not much more. Intelligence is the ability to overcome problems and adapt to new situations and is a broad set of coping mechanisms.
Education indeed does not equal intelligence, sure, there's a decent correlation but a lot of slack can be picked up by simple plain hard work. I've spoken to a psychologist from a well known dutch assessment center and she told me only half of the people with an academic title really have an academic level of performance.
It's been said that people can be express genious within their limitations
The idiot savant idea I presume, in many cases the basis is obsessive behaviour. The number of idiot savants is very very small, thanks to the movie "Rainman" people believe that every autist is a genius that can count. Excellence doesn't require intelligence, rather perseverance and attention to detail. Intelligence won't hurt but it's not a prerequisite.
It seems more common to meet 'smart' people who underachieve than otherwise.
Hmm I've met more people that surprised me of how far they've come with limited intelligence. "Street smarts' is such a phenomenon, a good understanding of human nature can get you very far. There's a lot of people in management positions that really have no business there, result of favoritism.