I bet now that the WoW Token is implemented in Wrath Classic, Blizzard will suddenly start actioning all the players who continue to buy third party gold. Now that these third party gold sellers are competition to Blizzard, those that buy from them are not buying from Blizzard and thus not giving Blizzard their cut of the sale.
These bans will probably will only be for a few days or weeks with the gold being removed so that they can come back and rebuy that gold the right way, in game, where it is now allowed, where Blizzard gets $5 for every transaction segment.