I think the question clearly ignores the recent understandings made by psychologists of the variety of intelligence that can be found in the mind.
Being that I am not particularly mathematical in my thinking, I have had quite some difficulty breaching the Prince difficulty (win very seldom, but that's what makes it fun and challenging!).
As a more imaginative and creative person, I find I have more fun sort of getting into the role and the historical story of my civs.
Anyway, other people are more mechanically intelligent and don't have the imagination and patience to be interested in video games very much, preferring to spend their time in the real world. Others are more socially intelligent and prefer the political intrigues of their own circles of friends to that of Hateshepsout and Tokugawa Ieyasu.
There are 14 types of intelligence identified by psychologists, which is one of the major fallacies of the IQ test (not to mention racial/cultural favouritism). I'm sure that people who have greater aptitude for a particular 4 or 5 of these are drawn to a video game like Civilization.
Furthermore, of the 4 or 5 which draw people to Civilization, each of these types of people will play the game in a different way, some will become incredibly bored with a peacful game, some will work harder than others to achieve high scores or beat the game on higher difficulties, and some prefer the modification and customization aspect of Civilization. In this way, I would say that Civilization appeals to many intelligent people, but I would consider it incorrect to assume that somebody who plays Civilization is MORE intelligent than somebody who doesn't.
I've been around Civ Fanatics since downloading mods for Civ2 at least as far back as 1999-2000, this is my first post on the forums. Looks like a great community here and I look forward to interacting with other fanatics like me!
