Go America. I can't speak for others, but I played Fable and tried to be good-ish I guess. Itold myself I'd play it again and be evil, but after the ever-so-dissapointing ending I said screw it and stopped playing it. I can honestly say that the ending to that game was probably the most anti-climactic, terrible written, and poorly presented endings I've ever had the misfortune of playing. That by itself is probably why I will not get Fable 3.
As for the topic, I think it's cause Americans try to act good in real life but suck at it so they end up just saying screw it and being assholes. In games, however, morality is little more than a quick-time event with a frowny face for pressing X and a Smiley face for pressing Y. Americans look at this and say, "Hey! I can be morally good and not have to sacrifice anything of true value!"