They also don't have fingers in modern / contempory, russian revolution, stone age, high-magic multi-planar fantasy, WWII flight sims, bloodstream-based anti-viral warfare, etc etc you get the point.
You could quite literally make an MMO where players select and play as pieces of fruit and as long as it was dynamic and engaging and rewarding then people would flock to it. Yes, another post-apocalyptic MMO would threaten P:V13, but only very marginally moreso than any other type of MMO.
At the end of the day, most people aren't really purists, and will be willing to shift their tastes and adapt to a new setting if it means a significant improvement in quality of gameplay. Competing with other products will be difficult but as my good friend Jane Austin once said, "It is a truth, universally acknowledged, that a good MMO in possession of a sizeable player base must be in want of some shoddy competition."
Competitors are only bad if their product is better than yours
Maybe you'll sit and sigh, wishing that I were near
Then maybe you'll ask me to come back again
And maybe I'll say "Maybe"