Here, then, are the differences I have surmised between a Rock Band and a real band:
Setting up your gear
Rock Band: Easy. Pick up your feather-light instruments and plug them into your Xbox with a USB cable that you should know how to use even if you've never seen a computer.
Real band: Easier. Especially if a roadie does it for you. Or insanely more difficult if you are your own roadie and you have a fused vertebrae or slipped disc from schlepping your gear across the country.
The playing experience
Rock Band: Tetris meets Simon meets karaoke. You need to have hand-eye coordination and be moderately literate (if you are the singer). There are no monitor mixes to fuss with, and your sound is consistent. Actually, your sound never changes, which kind of gets old. However, if your band messes up, you are mercifully and magically removed from the gig and you get to start over.
Real band: It's hard to beat the visceral high of playing live and creating something spontaneous. But if your band is having an off night, you still have to stand there in front of a crowd and finish the set.
The band dynamic
Rock Band: Volatile. Skill levels can vary, and though each player can select his or her own level, it's frustrating to get stopped in the middle of a song due to someone else's screwup. You do get three chances to bring a player back from the dead, which, sadly, doesn't happen in real life.
Real band: Volatile but with far more payoff. And band fights about set list order and how the guitar is always too loud are more justifiable than fighting over someone accidentally hitting the "pause" button in the middle of a song.
The touring life