Gamma asks: I'm sure a lot of people have been wondering this, but why can only No Mercy and Blood Harvest be played in Versus?
Chet Faliszek: Versus maps, while appearing near the same, are actually different versions of the maps. So for L4D we shipped with a total of 30 maps. The versus maps have to be split off so we can playtest and adjust them specifically.
In co-op, a section that is hard for Infected is easy for the survivors, it isn't unfair, it's just how that map plays. In versus, though, it becomes unfair, or just isn't fun for the Infected.