Originally Posted by MN Tigerstripes
Otherwise from what I've heard and seen some horses have the "hair" gene and some don't.
I can vouch for this - one of my mare's tails grows like mad if you just brush it every few days, the other, it doesn't matter what you do, her tail will not grow a centimeter! I also had a mare several years ago who had a short tail, it didn't sit past her hocks, and the whole 8-ish years I had her it didn't grow either.
So I would argue it does depends on the horse - not the breed - because I've only owned QHs and I've seen drastic differences from horse to horse.