It's completely possible that Guitar Hero and Rock Band could steer someone toward "real" music that might not have been otherwise.
My stepson has never shown an interest in classic rock tunes until he started playing songs like Mississippi Woman and Sunshine of my Love on Guitar Hero. And for his birthday he wants a "real" guitar because he wants to learn to play "Welcome To The Jungle" for "real".
You can say what you want about the games but it is a fact that the popularity of the games has given rock music a little bit of a resurgence. And that is not a bad thing.