I have to agree with mildot, and my hubby is a pro triathlete who goes on 4-hr long road bike rides at a ridiculous speed ;) BUT he has enough sense not to ride in the middle of the darn road and he would NEVER go flying past someone on horseback...and he doesn't ride. He just has common sense. I used to do Tri's myself and when I would go out on a shared trail to ride my bike, I ALWAYS alerted those I was coming up on by saying "On your left" far enough ahead for them to look back at me and know I was coming, and I would slow my pace as well.
For horses, I would ask permission to pass, knowing that some are spookier than others and I always received "You're good, thanks!" No one ever told me "NO you can't pass me!!" They just appreciated the heads up for themselves, to ready themselves in case their horse spooked. Had I gone shooting up the horse's side and he kicked me in the face, it would have been my own darn fault for being a moron.
Same thing with dogs on trail...I don't go blasting past someone's dog either, JUST IN CASE. What if the dog gets scared and attacks me? Or what if it's just an aggressive dog in general? I stay out of leash-range with anyone's dogs. If I ran right up on one and he bit me, MY FAULT not the owner's and not the dog's, given he's on a leash and under control of course. I hate when people place the blame on the animals for their own stupidity and carelessness.
I teased my dog once when I was a little kid, because I thought it was funny. She bit me in the face. Did she get in trouble? NOPE...did I? YEP for teasing the dog! And I deserved it! It was my own stupidity that caused the reaction I got. People need to show more responsibility for their actions.