Prior to the patch preceding WotLK, a Paladin could AoE (Consecrate) to hit as many targets as were in their radius. They could also Holy Block and Blessing of Sanctuary, to inflict a lot of damage on any creature not behind them. The Paladin could effectively kill any number of mobs, provided they had the health to survive.

With the patch prior to WotLK, a druid can hit as many targets as there are with a Swipe rather then hitting only three. Warriors and Deathknights also have effective AoE tanking now, which they did not have prior to this.

At this point in the game, any tanking class will be an exceptional booster. The reason people used to say you needed a Paladin, is mainly because they could kill 50 mobs at once, while the druid or warrior could kill 3 at once.