I agree with Chris Mood on the bordeom thing and I think the reason for that is that a song would just sound too 'busy' if both guitarists and bassists were playing complicated pieces at the same time...so just leave it to one...thats what I see atleast...I know in my band whenever I am doing a solo the bassist gets damn bored, as do I when he does a bass solo or slapping groove. I would just sound like too much was happening if it was any other way, I guess