Actually, BL stands for Borderline even though every BL tier is essentially a "banlist" for the tier below it. We already have a BL and a BL2 Tier, Ubers is so big that it's shaping up its own competitive metagame, and there are a bunch of Pokemon who really aren't up to par at all with the rest of the pokes in that tier. Maybe after gen 6 comes out, a 'BL3' might be a good idea.
Lolz, I'm sorry but your ignorance here is SCREAMING. Sand Veil is banned because the
one being attacked is unfairly raising his chances of completely evading a move that would have normally killed him. Snow Cloak is
also banned for the same reason, despite Hail being the absolute worst ability and the fact that, even up to the time of its banning, Snow Cloak wasn't on a single OU-viable Pokemon. Hydro Pump and ALL OTHER MOVES IN THE GAME are legal because it's the
attacker who makes the choice to use these moves, comparing the risk of their accuracy to the reward of their power and/or effects. If you don't like Hydro Pump,
then don't use it. You have no choice in the matter of facing someone else's Sand Veil Garchomp. Like, really, these two aren't comparable in the
slightest.
Bans are for keeping smart/lucky people from using broken tactics, not encouraging dumb/unlucky people to make smart ones. Nobody cares if multiple people use Hydro Pump and miss because it's their fault for running that move.