if enough people on horses fall off and die, the average could still win over the population. I don't have the original statistic I saw in front of me, but that's how I interpreted it.
and in agricultural times in the US, I'd say most people were on horses.
I wonder if this is more a wild west pulp fiction meme, than actual reality. A lot of people today are collateral damage of cars, getting maimed, mutilated, crippled, killed, it's pretty indiscriminatory, drivers and bystanders alike suffer its consequences. It's hard to believe horses had the same blast radius proportionally speaking.