Due to itemization and abilities, Warrior and Paladin tanks currently have a greater ability to avoid Crushing Blows than Druid tanks. In the near future, this may become a moot point. Khurg of Spirestone, a Tauren Warrior, worries that Warrior tanks may become somewhat obsolete with the removal of Crushing Blows from boss mobs and a potential thirty second cool down on Shield Block. He asked "What will be the purpose of defense in WotLK ?" The following response from Rawglrlrgll of Lothar was that the defense statistic prevents critical strikes and still buffs the chance for avoidance.
A discussion ensued about the role of tanks in Wrath of the Lich King. Fungus of Altar of Storms responded that each of the four tanking classes in Wrath will have separate foci. Warriors will be mitigation tanks that rely on evasion at the armor cap. Paladins will have less armor than Warriors, but will continue to AoE tank. Death Knights are slated to rely on resistances for tanking. Druids will become less viable as main tanks, but will still serve as off tanks. This is seen by many Druids as getting "the shaft."
Some suggested taking a passive approach until Wrath is released, but others feel that if they don't speak out now, changes won't come until months after the expansion. From what we've seen of Wrath so far, do you think the face of tanking is about to be changed forever?