I hear alot of people saying that guitarists don't learn notation because they're lazy. Honestly, that's usually far from the case. Sure, it began as a crutch, but for many musicians it is now possibly the only real way to do it. Truth is that it's much more difficult to find notation online or such than it's ever been to find tablature. I'm not really justifying it, but you have to understand that most guitarists don't learn western notation because they honestly can't see how it'd benefit them.
But, I was in a band last year where only the keyboardist and sort of the bassist and drummer (they knew western notation on other instruments, but not on their own) had any real idea of what music really meant. It makes rehearsing very difficult. For instance, if we wanted to start from a certain measure in the song, you would not be able to just say the number because no one knew what number that was. Vocal harmonies were almost impossible unless you talk it note by note, given people didn't know how chords were formed. Guitarists were unable to create solos, needing instead to just play them exactly as the recording had..
It really doesn't have to be western notation, I guess, but everyone needs to learn the same format of music to really understand what the others are doing. Western music tends to promote that pretty well.