Well I have never seen any results my self however I would have to say from the term middle-class in sociology most who play RPG's are not. An average of any gamer I know of ranges all over the place colleges which are conformity methods for middle class are good places for role playing however the military is one of the largest places of gamers out there. And the beginning pay for us soldgers is considered lower middle class. As well I wounder if role players are more predominate at 2 year community colleges or at four year ones.
See also this thread (http://www.indie-rpgs.com/viewtopic.php?t=13618); Wizards' current market research estimates 4 million monthly D&D players.
Ken Hite also does a yearly State of the Industry (http://www.gamingreport.com/modules.php?op=modload&name=Sections&file=index&req=viewarticle&artid=96), based on data from Comics & Games Retailer Magazine.
The above two posts were split from Size of the RPG market? (http://www.indie-rpgs.com/viewtopic.php?t=5516)
Best,
Ron