I'm a little confused as to why you think that Fury isn't primarily a PVP spec.
You have Improved Berserker Rage and Piercing Howl.
Berserker Rage is a HUGE ability to have in PVP.
Arms is fine against PVP / so is Prot (against Casters) but if I was doing PVP I would definitely be Fury specced.
What am I missing here that makes Arms a better PVP spec?