The first truly excellent reply.

Not all fiction is a good way to escape, but you need to look at what kind of fiction I am talking about. I would call it heroic fiction. LOTR, SW and so on. This suggests being unhappy with one's self.

The math and machines and even software and Linux part: this is IMHO only partially true. I know many non-STEM nerds. Most STEM nerds have some interest in fantasy but not the other way around and IQ may be one of the factors.

I know more people who read and fantasize about D&D rulebooks than people who gather the courage to play it socially.

Having said that, a "social alliance of social outcasts" is a non-typical kind of socializing.

STEM-nerdy interests correlate with IQ, escapist-nerdy ones not. Have you ever read the Dragonlance Chronicles, the No. 1 fantasy of my youth? Point is, it is not actually difficult or complicated. Watching Game of Thrones is leaps and bounds harder, so many names and faces.

Further confounding: indeed children from poor broken families are less likely to do this. What escapist-nerdiness perhaps correlates with is not IQ as such but more like family background where reading books and related activities are respected and pushed by parents. Intellectualism, in a way, bookwormery, but not necessarily IQ as far as escapist-nerdiness goes. STEM-nerdiness is indeed IQ.

Interesting: in Europe, families with a more or less secular Jewish background went from worshipping The Book to worshipping "books". Literature, reading, intellectualism. Kids of this background were over-represented in this in my experience, because of the family being very approving of bookish stuff. This is intellectual, but yet not necessarily high-IQ. It is closer to liberal arts than hard-sciences, and indeed the most typical career here is historian - a certainly lower-IQ-requirement one than math.