Here's the tldr version of what defense warriors need to be uncrittable in WotLK at level 80. You can find it lots of places, but I wanted a short quick reference.
Defense skill needed to be uncrittable = 540
Warrior base defense skill at level 80 = 400
Defense skill needed from gear = 140 (689 defense rating)
1 Defense skill = 4.92 defense rating
1 Defense rating = .2033 defense skill
Resilience also contributes to crit reduction, but I've never been a fan of needing PvP gear for PvE content when I can do without it.
While it is often called defense 'cap' it really means defense 'minimum' since you shouldn't just stop at 540, especially due to diminishing returns at level 80 of pure parry/dodge/block stats.