I'm sure it happens more then we hear. I've known of several bad accidents just among the people I know. The thing is almost all of the accidents where carelessness, or recklessness on the part of the person hurt. Then the horse gets the blame, and people who don't know better are afraid of them.
Kicking and biting horses need an immediate and pretty severe response. It's unacceptable behavior no matter what, but sometimes I understand why they do it.
Becky
As usual, you are right on. Not that many bad horses, just careless people. And the true biters and kickers need immediate and attention getting discipline.