Median Damage that comes close to the damage a tank gets doesnt exists, this is the main problem in Healing in TBC.
Your Maintank Healers can overheal 70% of their heals(pure spamming) and the tank can still die. In Sunwell we quite some times had tanks dieing because of massive spike damage(over 20k in under 2secs). Preventing that is pure luck as "coordinating" healing on the tank is impossible because of haste gear(and haste procs) and random lag. A Maintank currently always needs full healing on him the only thing you can do is aborting heals manually in the last sec although that kills Maintanks sometimes aswell(getting dmg right after the heal is aborted).
The problem arised because Tanks could easily stack up high parry/doge values and to make a fight "hard" instead of trivial on the Maintank Healing the mobs got massive damage, that rapes your MT if he doesnt dodge 4hits in a row. You can clearly see this because every SWP Boss has a hidden buff on him that removes 20%(!!!) dodge from the Tanking Person. While in Black Temple a renew is almost enough to heal your Maintank...
It looks like they want to go away from Pure Spamming in WotLK, which healers appreciate I guess.