I'm not sure whether the following traits fit into your working definition of the stereotype, but I've frequently read WOTC published materials which offer that many gamers have a natural shyness and confidence issues which they might need to overcome for more successful gaming, pointing out that wish-fulfilment in people feeling robbed of power in the real world is a major driver for gaming. Such sources seemed to feel it important to offer advice on getting enough sleep, eating healthy and making sure to take care of basic heigene... It would seem that they have an opinion about the makeup of the average gamer. It costs money to produce that stuff, and I'm left wondering whether that is a confident investment WOtC makes because they feel a large part of their market is dysfunctional/abnormal/adhering to the stereotype. Does this reinforce the stereotype, or was that type so apparent to them they felt the need to offer such embarassing advice in their books? DMGII (3.5) was a good example for some of that stuff, and I know there was more too. I can't remember those sources off the top of my head, but will post them if I come across them.
I have a small group of friends I game with which I met from non-game-related situations, and I guess we'd fit more or less into the proposed normal as defined in terms of your research question. There have been a couple of occasions where I've gamed with groups from gaming stores/societies etc. and certainly have found a number of really odd folk. Some were a bit out-there, but lovely. Others were just... something. Not all of them though. And many of these convention class? gamers, apparently well adjusted or not weren't gaming at the store because they were transient for whatever reason, but because there was no other way to play.