Well, the major reason to have a bard in the party is to use lore to identify magic items, which means he needs high scores in both int and wis, and cha is his primary attribute, and he's dependent on dex, and needs con to be able to survive the hits he can't avoid... Bards have mad MAD. And if you need to have 5 high scores to be useful as a bard, it's only fair to let other NPCs have high scores in all of their stats. And then there's the fact that a lot of items have minimum stat requirements. For example, Viconia can't wear plate mail without a strength-enhancing item of some kind.