The problem is not Mario being a casual game or not, the problem is developers thinking, casual game = crappy quality low budget game, and thats not true, a casual game is a game created and advertised with the purpose of creating interest in a not so game friendly market, and thats the point of the ad, the ads are saying "Hey, you can play too" and that is the key of wii succes, not Mario, not fitting games, and above all not the controller gimmick
Nintendo is the best videogames company ever!