True, but that's not very rock n roll for one, and then of course a million people would jump all over them with even more accusations of using excessive tracks. They way they are doing it is fine. You could say that about any band that has a second/rhythm guitarist then, why even bother having one, just use a track?
You can make the same argument for alot of the sounds coming off the U2 stage...some of the elements of the background music, for instance, aren't all that audible at all once the band fires up. Why bother at all? (well, for one, they probably like hearing them in their IEMs, so that the song sounds like the song as they know it and wrote it). Why bother having Edge sing a backup that sounds like him + 100 voices (ie Beautiful Day) why not just have a track? etc etc
Why does a basketball player slam dunk the ball on a fast break when a layup would do the exact same thing ie 2 pts?
Have another theory about singers playing guitar even for just minor parts..here's an emotion I've felt fronting a band sometimes: Sometimes, after doing a number of songs and being out there interacting with the crowd and the band is interacting with each other..well it's almost like there's a disconnect where it's a singer + a band instead of one unit: a band. Not sure how to describe it but it's like..you want to be "part of the band" again..when you put the guitar on, you get grounded right back into the sound coming off the stage - well you're also fairly limited in where you can go on the stage too, once you put it on. I don't know if there's any other singers here that can identify with this but I know 2 or 3 others (non-U2 guys) and we've talked about this and they concur that they value the songs where they put on their guitar because it feels more whole as a band again. Maybe Bono gets that way too, who knows? We do know that he originally wanted to be more part of the music ie guitar player, than singer, so maybe he just has moments where he needs to be a part of the music again? Especially in songs where he maybe played in the studio or as part of the writing/practicing process, I can definitely see him feeling sortof naked or like something was missing on those songs without a guitar on stage if he always had one kicking around the studio/practice space. I dunno, just something that occurred to me after practice the other night..