Rock Band is air guitar.
That's all it really is.
When you listen to really good music, you Air Guitar.
All Rock Band does is put something in your hands while you Air Guitar.
It will never really replace the feeling of actually performing real music, and if a potential beethoven of rock wastes their talent playing Rock Band because it's easier, then we didn't need them.. There'll be a little Mozart around soon enough who'll blow that loser out of the water anyway.. and he'll play a real instrument.
all of that being said, I love Rock Band.