Ok, don't laugh, and here's why:
For the oldsters and aging hippies out there (you know who you are), you get to "play along" with classic tunes like Thin Lizzy's "Bad Reputation" and Sabbath's "War Pigs," plus some new classics like "Woman" by Wolfmother.
For the youngsters, it's a great way to introduce pure "rock," that gets them away from the idiotic junk that's on so many of the modern radio stations today. I love watching my 13 year old nephew jamming to "Institutionalized" by the Suicidal Tendencies and say how cool the tune is.
Ok, who plays one of these games, or the similar Rock Band? Fess up. Me, I play GH II every couple of weeks, and can just barely finish a couple of songs on the hard level.