PVP and Expertise RatingFollow

Expertise isn't exactly something you focus on in PvP, since you should almost always be behind your target (and making a strong effort to remain so) your opponent should never be able to parry or dodge one of your attacks.

Of course there will be times where your stuck face-to-face with your target and a few dodges and parries will go off, but this really only applies to certain classes (warriors, DKs, Pallies, and other rogues for the most part, hunters too but theirs is meh) and shouldn't be focused on.

Not only this, but reaching the expertise cap for other players would be incredibly difficult, since everyone has a different chance to parry (most rogues have 5-11% where some DKs I've seen running around have around 20% or more)

And though I can't confirm this with any hard data or anything, I'm fairly certain that EP values in PvP don't really apply, you should use your best judgement in choosing your stats in regards to PvP (High crit is less valuable against targets with high resilience where AP isn't effected, for example)