Well, I'm not sure we're more builders than, say, the Japanese or Germans. I honestly do think it is because we lack the medieval experience, specifically. We have no stories like King Arthur, where history and fantasy are mixed up inextricably. I feel pretty stronger it's the American lack of that that makes it hard to write distinctly American fantasy combined with our extreme technophilia. But it can't just be the technophilia, because Japan is even more absurdly technophile than we are, but they have a lot of Japanese themed fantasy -- because they, too, had a dark age where legend and history gets mixed up.

But the reason I said conspiracy theory instead of comic books is because the same sort of mixing of fact and the absurd happens with conspiracy theory as it does with legend. Oh, comic books routinely produce the most iconic characters in American literature, but no one past the age of 8 believes in Batman -- but a lot of people believe that aliens come down and probe people, or slaughter cows, or make art in fields, or even have replaced the government with robots. Like with King Arthur or Robin Hood or Roland, they can't seperate fact from fiction.

(And, for what it is worth, comic books are far more sci-fi than fantasy. Almost all the popular and successful characters have sci-fi backgrounds and the number of sci-fi stories strongly outweighs the number of fantasy stories, in large. So comics are more sci-fi with some fantasy than the other way around, for what it is worth.)