Please note that this [b]only applies to normal melee hits[/b], aka white damage. [b]Not yellow damage[/b]…yellow damage comes from special attacks and use a different calculation methodology all-together.
Okay, I think some people are confused about what exactly a crushing blow is and why it happens: A crushing blow is a hit that is 150% of normal damage and can only be dealt by mobs (not by players). It occurs whenever a mob has 15 or more points in Base Weapon Skill over a player’s Base Defense (in other words, a level 73 mob vs a level 70 player :P).
So if you have skilled your character’s Base Defense out to 350 (base means 350 WITHOUT any gear and WITHOUT any talent bonuses), only a mob with a Weapon Skill of 365 will be able to hit you with a Crushing Blow; in other words, a mob of level 73.
Also, remember that all possible attack outcomes on your character are mutually exclusive. In other words, a block is a block and a crit is a crit. You cannot block crits or dodge crushing blows….that is simply not the way hits are calculated.