I would personally argue that the casual 'non-gamer' gamer came into existance soon after videogames became mainstream with the release of games like Pong and Pac Man. Starting with the NES, each generation has grown dramatically larger mainly because videogames became a much more inclusive activity and new demographics began gaming ...
Sony was really successful with the Playstation because its release was well timed to capture the growing market of teenage boy and young adult male gamers, and to capatalize on the mistakes of Sega (32X, Sega CD, Saturn) and Nintendo (Virtual Boy, N64). They continued this strategy with the PS2 with being a little more inclusive and targeting a slightly older demographic and (due to lack of disruptive competition) were successful; but since they did not really target a dramatically larger demographic the growth in the industry during the PS2's generation wasn't as large as the growth durring the Playstation generation.
Nintendo didn't create these gamers that they're marketing to now, many women between the age of 18 and 40 have played videogames for a long time but they have never been marketed towards, and a lot of men in their late 20s and 30s now have young families which they would like to play videogames with. Nintendo has been so successful because they realized that over 50% of the market is not having their needs and desires met by their competition.
