Blizzard announced today that there will be several changes coming in the next little bit due to rule changes. As of the next patch all of the current raids will become easier as per this message from Borrnak
To coincide with the upcoming new talents and mechanic changes for classes in the next patch, we are making some adjustments in existing raid content to provide a smooth transition when the upcoming patch is released. The creatures and bosses in raid dungeons that were introduced in The Burning Crusade will have their health reduced, and most will have their standard melee damage output reduced as well, but their spell and ability damage are not being changed. These changes are being made in all raid dungeons from Karazhan to Sunwell Plateau as well as the outdoor encounters of Doom Lord Kazzak and Doomwalker. On top of this Illidan is also doing his part and will stop casting Shear on players.