I'm kind of curious as to how accurate the age break down works out to be. I will agree that, speaking broadly, you can separate gamers into general categories of "young", "middle", and "old" which will tend to have roughly the psychological profiles outlined in your post, particularly the tendency of gamers in the middle group to be disproportionately attracted to games and characters which are dark and/or rebellious. However, my impression has always been that the age ranges are somewhat lower here than where you peg it at, with the traits of the "middle" group mostly falling in the 12-18 age range and then tapering off into something of a gray area.

Granted, as far as I'm concerned World of Warcraft is--like the African savannah--territory that's best viewed from afar, with a good telescope. Thus my up-close experience is rather limited, and for all I know WoW's demographics may very well work out a bit differently from what I commonly observe in the more provincial areas of gamingdom that I tend to frequent. Nevertheless, it would be my guess that any disproportionate tendency towards the Horde in the 18-26 gaming crowd (particularly the mid to upper portions of that range) is probably more attributable to a sense of novelty than to a general sympathy for "evil" races/characters--most experienced gamers I've known in the 20+ age range tend to be a bit jaded and often interested in trying things that are new or atypical, and the Horde's race selection is a bit more unique than the still rather Tolkeinesque offerings of the Alliance.