Ditto to you, sir.

In Vanilla the only way to become uncrushable was to stack avoidance to push crushing blows off the boss' attack table.

0% 100%
|--Dodge--|---Parry---|-----Block-----|----Norm. Atk----|-Crsh Blw-|

Attack tables looked something like that. Increasing block pushed normal and crushing blows further over. Attaining a certain level of avoidance insured that a boss' hit table had Crushing Blow change well over the 100 mark, IE "pushed off the attack table". Imagine every attack as rolling 1-100. If you push the "roll" required for Crushing Blows over 100 by stacking Dodge, Parry, and Block chance, it can't be rolled anymore.

They eventually changed Crushing Blows so that only mobs 4 levels higher can get them, meaning bosses could no longer get them (They are always 3 levels higher). The attack tables were then changed, essentially replacing Crushing Blows with Critical Strikes, and Defense Rating became the required way to push Critical Strikes off the new attack tables.

That is how it was for most of Wrath. No Crushing Blows period, and tanks needing 540 defense skill to become uncrittable. Crushing blows and critical strikes are NOT the same thing.

Get YOUR facts straight.