It's probably a combination of intelligence, maturity, and patience, I think. Players who stay here are either looking to do some sort of fantasy roleplay, or cerebral challenge I suspect, neither of which is likely to appeal as heavily to your typical kid, as Fallout, or such. There are people on the forum who do not come across as very smart, or knowledgable, but you get a few of those everywhere.
Damn, that was the other point I was thinking of. The way I see it, Warlight is like a mix between chess-style strategy and RPG-style imagination. I think it attracts both types, and you can play it on the extreme-strategy side of things, and on the extreme-RPG side of things, or somewhere in between. So, I think the people you're referring to as 'not at smart/knowledgable' are probably more attracted for the historical/fantasy-battles/RPG aspects of it than the out-think-your-opponent/strategy aspects of it.