If you play a mage/tank/healer combo, you'll also have the advantage, from the mage's point of view, of being able to opt for dps pets, water or fire, which you seldomly use for soloing usually. So your own dps will be raised.
Also, you or your healer will barely draw aggro, pet will be high on aggro list all the time, even if it doesn't have consequences on tanking, as mobs will always prefer a PC over a pet if in melee range. However, think of turning pet's taunt off, so your tank, when needed, can reposition mob/himself without having to worry that a taunting pet grabs aggro when he tries to move the mob.
Of course, never use an earth pet because of the root aggro problem in that combo (if your healer stands close to the tank and therefore close to the mob, he could get hit when the mob is rooted). The air pet would be of some use only when you absolutely need a mob to be stunned at intervalls, but you lose all the other benefits of an air pet in your combo (high AC etc.), except if you are in a situation where you know they will be adds and your tank can't handle them for some reason (level, low on health, healer died, whatever), then you can use the air pet to offtank an add in combination with gargoyle (Raging Servant line) when at level 70 (try to always send gargoyle before pet if you can so it keeps aggro for 18 sec). In this case, of course, you need to move your tank so that add sticks on pet(s).
I hope this helps a little bit for your uber combo
