(All of this coming from a Melee player, mind you)
I'd have to agree with Pokémonrock. The Smashboards poll is about the SBR rule. Y'all could come up with your own ruleset.
As for MK himself, I understand WHY he's so debatable. Disgustingly good recovery, very spammable attacks with little lag, etc. etc., but I don't see why he should be banned. Yes, he is the ONLY character in Smash history to receive a perfect score on an SBR ranking (he got a 15/15...Melee Fox only got 9.9/10), but he's not unstoppable. I say don't ban...granted, I don't play Brawl, so it doesn't matter but so much...still, I'd be even MORE disgusted to see Smash get its first ever character-ban.
And P-rock, I hate to use tier-list logic, but the reason Sonic isn't banned is because, on a high-competitive level, he's not all that good. I'm no pro, but over the years, I learned to accept what the SBR says, since they tend to be right, and are on a much higher level of skill than myself. Last I checked, Sonic had a single-digit score out of 15. He might seem cheap to people that don't go to a lot of "official" tournaments, but in that "official" environment, he's quite managable and weak.
EDIT: I just checked the tier list (good thing y'all have it posted)...Sonic has a 4.16 out of 15...that's...ouch >_< that'd be why he's not banned.