Making powers behave differently in pvp and pve is a poor mans fix to the real problem - superdumb AI, if npc's behaved with the kind of versatility and ingenuity of a player powers would demand comparable influences on a battle.

Conceptually and stylistically powers need to behave the same in all scenarios, this is a sad concession that could easily spiral out of control.

Whats needed in MMO's is a seemless transition between pvp and pve so the player who so chooses never knows the difference.