One of the accepted facts of raiding life used to be that the main tank was the guild's gearing priority. As Adam Holisky's observed, "Everything that happens in the raid eventually makes it back to the tank." Healers undergeared? You're screwed. DPS incompetent or just badly grouped? Buh-bye. Random number generator wreaking all manner of havoc on healer crits and boss parries? Thar be the graveyard. A truly cynical mind would opine that the tank should be as well-geared as possible if only because it makes it easier for the raid to forget that person existed as anything other than a rapidly-advancing line on the Omen screen that: a). always stayed above their own, and b). never died. There are enough random variables while the raid's learning a new boss that the tank needs to be eliminated as one, and in vanilla WoW that was certainly the goal. Raid and offtank damage on most encounters hadn't scaled to the point where you could make a compelling argument in favor of gear equilibrium across your tanking roster. What was the point of something like that when 95% of the damage in a fight was going to be absorbed by a single person?