If your primary play is battlegrounds, instead of arena...
The Ret Paladin is a good addition, in that they add a lot of utility to a composition.
But they don't have the burst that a lot of others have, so are often seen on a 10-box more than a 5-box.
The utility is nice, and with 10 you have the firepower to kill quickly, even if not everyone is as high on the DPS.