I always said, there is no defense-cap... well actually there is.
When your total dodge+parry+miss=102.4% you have reached the usefull defense-cap.
This thread on Maintankadin (here) delves into this further completely useless information.
Unbuffed Defense-cap is 7491 defense-rating = 1532 defense skill
Raid-buffed cap is 7083 defense-rating = 1440 defense skill
So next time someone asks me if I am defense-capped, I just say that I am...what??? 900 short??