I almost bought Rock Band because of the Beatles (and may still get it for that reason). I wasn't thrilled with most of the songs typically available, but Beatles! WoW!
If U2 were able to come up with a Rock Band, I'd defiitely get that.
My only question is how to play U2's songs given Edge's many effects (especially the echo effect). Would that delay effect be built into the system, would it be a feature on a special guitar (or pedal?)? Could this even be a reason for U2 not releasing it?
As for this "sell-out" argument... I've always supported the notion of artists using their music for music related events. For example, having their music in a movie, in commercials advertising their album, in iTunes or iPod commercials, etc. To me, Rock Band is part of that. I would argue that if anything is close to selling out in the U2 world, it was the Harley commercial Larry did in the late 80's and the current Blackberry ad (but this latter one is acceptable given that Blackberry is sponsoring the tour, helping to keep ticket prices down). In other words, I think if U2 can do iTunes and Blackberry and Harley Davidson ads, then Rock Star is not selling out at all. It's just a great way for a new generation of fans to discover their music (and for us old fans to have more fun with the songs we love).