To allow people who lack talent or skill to feel for a moment like your favorite rock star. I generally like the games though I feel they are being marketed a little too aggressively. I just read about Guitar Heroes V and I don't even remember Guitar Heroes IV being released.

I was also surprised when Rock Band 2 came out a year after the first game was released which seemed really silly to me. Some people just get overly obsessed with games. I remember all the media fire on Everquest and WoW.