I'm no expert but I can imagine the reason why tank gear isn't as important as dps gear for savage content is because bosses focus more on their mecanics and cause the group to react. Better gear for the majority of your party (the dps) means they can take a little more pain for their mistakes. An adequately geared tank will still survive a tank buster if they use their cooldowns well. It also means healers don't need to heal as much, keeping their mp up for when it's needed.