I'm American, and I ****ing love this game. I've played since original Mount & Blade beta version 0.751.
Most of my American and European friends dislike Mount & Blade, and the reason why is how unpolished it is (and always has been). I love the feel of the melee system more than any other melee system I've seen, but the combat doesn't look as good as games with more fancy canned animations (but less player control). It seems that most gamers, regardless of culture, prefer games where the combat looks more lifelike, even if it feels less lifelike (that is, even if the player has less control and is more watching than doing).
And it isn't just combat, but the Mount & Blade series is rough-around-the-edges in general. I see it as a diamond in the rough, but I think most people just see the "rough" part and don't give it a proper chance.
All that said: I wouldn't be surprised if metrics showed that there were in fact a proportionately higher number of European players than American ones. My experience in hardcore flight sim-games (a high-difficulty genre) showed that there was a higher percentage of European players than American ones, and so I think there is something to the OP's suggestion that American gamers tend to prefer less difficult games than European gamers, on average. And while Mount & Blade does have options to reduce difficulty, the melee system is inherently more difficult than most game's melee systems. (That's the point of the game, isn't it?)