There are people around here who believe that their interest in computer science is one of the things that makes them smarter than other people, but that is not a belief I am defending. In fact, I believe that is a small minority of people here. Most of the posts I saw in this thread were criticizing the education system that leaves many people without an understanding of compound interest, not calling those people idiots.
Most people are comfortable with the idea that some people are at the bottom of the intelligence heap. It is scientifically verifiable that some individuals are unable to remember new information or identify patterns. Why shouldn't this be true at the top of the heap as well? Based on my life experiences, I believe that my intelligence is significantly above average, although I realize that I have been aided by fortunate circumstances. However, I am not strongly invested in the idea: I am more interested in being happy, in being a disciplined worker, and in having strong relationships with people than I am in being a smart person. Why are you so invested in the idea that no one is smarter than anyone else?
The ability to educate oneself is a privilege of one's enviroment, background and upbringing, the ability to do well in one specific area could be a measure of one's interests provided one has the freedom and means to follow it. None of these are a measure of one's intelligence. Individuals could go on to distinguish themselves in their respective fields and then could be part of a group of say nobel winners or some specific measure.
This 20% seems completely arbitary and self serving that puts you in a group simply because of your specific interests or chosen profession. This is not in the least scientific or valid and there appears to be no useful purpose than hubris. The bigger problem is why the great need to feel better than others and clutch at shadows? This is how bigotry works.
Surely every human being has the ability to learn and be adept at what they do given the right conditions and this is a problem the world grapples with, to provide these conditions.
An individual struggling with compound interest is an opportunity for those who know, to try to teach them in a way they can understand, not an opportunity to deride and run them down as idiots. That's juvenile and mean spirited.