Manners or the Lack Thereof

You've all heard me complain about the bike path.  Well, here I go again. 
Why is it so difficult for people to say "On your left" when they are passing??!!  Seriously!  It's not that hard!  Fancy bikes are really quiet and you can't hear people coming up behind you.  I swear, every person who passed me today (and there were a lot) didn't let me know they were there.  This is a safety issue and today was a prime example. 
One of the reasons the tandem works out so well for Stefanie and me is that, though Stef has everything it takes to be a good cyclist, she learned to ride as an adult and isn't super confident about steering.  One of her goals this summer has been to get out on a regular bike and build up her skills.  So, today was our big day to all go out on seperate bikes.  We were not out on the path five minutes when some idiot passed Stef real close without warning her, startled her and she crashed.  Fortunately, she knows how to fall and though she will have some really spectacular bruises and road rash, she didn't break anything. 
So, Stefanie gets to spend the day snuggled up to ice packs and eating Motrin all because some asshole couldn't be bothered to say "On your left".