Age of Conan game director Craig Morrison recently waded into the fray via his personal blog, and he says that defining PvP in an MMO context involves separating the wish for conquest from the wish for competition.
Morrison touches on several interesting aspects of MMO PvP, including a bit of history relating to the arenas and battlegrounds that are usually reviled by hardcore player types. "The needs of accessibility dictated that designers try and find a way to accommodate the appeal of the conquest style of play while also retaining the fairness of the competitive desires of the players," he explains.
Ultimately, Morrison offers a bit of hope for those who prefer open-world conflict. "It's great to finish a great story and storm the castle and beat the bad guy. It is something else altogether to get to keep his castle, and for you to become the bad guy for the next would-be hero to try and conquer," he says.