what gtsawyer said - any other type of protection is against any accident which might happen, but many people have and continue to get away without using it through careful work practices.
Hearing protection is against something which will almost definitely happen over a longer period of time. Ok, you'll get away with it once or twice, but use a saw constantly without hearing protection and you can wave goodbye to your hearing! There's no maybe about it, at least for most people. However, I'm sure there's someone out there who's been using saws for 50+ years and never had a problem who's going to pop up and prove me wrong!
cheers,
Joe