I think there's room for both. Speaking for myself, there are times that I can enjoy a good "casual" game that makes no pretense towards immersion and other times that I like losing myself in another world. Both have their draws; the casual game is a great release when you just want to have some fun and the immersive game is the perfect escapism from your boring, humdrum life. For example, on the Xbox 360 lately I'll start out with a couple of quick games of Uno before diving head-on into Fallout 3.

While it's great to examine roles of various games I think this is a non-issue. There will always be both types of games, there will always be developers for both and there will always be people who want either type of experience at different times.