Crushing blows as a mechanic are rather severe, but thats the beauty of them, do you generate more threat (rage / mana usage) or do you stay uncrushable? Fights like the prince are interesting because of both the crush mechanic and the attacks like flurry (watching someone get crushed 5 times in a row is hilarious to watch

, especially when its for < 600 each time

.
With the deathknight I can see them needing to change this, as Druids already fill the high armour tank role, so a warrior type armour class vs crushing blows would basically harm the deathknight class as it would have a minimal role to play unless it has some major special abilities that allow it to negate crushes or similar. This is of course unless its designed as sothing like an elemental tank, which would basically be immune to your blocks anyway making your shield useless other than as extra armour / slots.
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Ahh, but you have heard of me.
http://eu.wowarmory.com/character-sheet.xml?r=Lightbringer&n=elyria