Even though "Vulcan" had the most votes, the IAU rejected it for two reasons. First, it had been the name of a planet that was thought in the 19th century to exist between Mercury and the sun, as a way of explaining peculiarities in Mercury's orbit. Einstein's Theory of General Relativity did away with the need for this extra planet, but these days, the term "Vulcanoid" describes an asteroid – also hypothetical – that orbits close to the sun.
Second, the IAU said that "Vulcan" didn't fit in with the mythological underworld theme that guided the naming of Pluto's four other moons. Kerberos is the name of the three-headed canine that guards the gates to Hades, and Styx is the name of the river that separates the worlds of the living and the dead, as well as the name of the goddess who guards that river.
Pluto's other moons are named Charon, Nix, and Hydra. Charon is the ferryman who transports the souls of the dead across the Styx; Nix is the goddess of the night who lives in a deep abyss in the underworld, and Hydra is a many-headed serpent who guards a lake that is an entrance to Hades.
So no Vulcan. The name is at once too familiar and insufficiently hellish. But, as the SETI institute's Showalter noted, its still possible that Star Trek fans might get a few craters named for their spacefaring heroes.
And yet, those craters are currently just as hypothetical as Vulcan and the Vulcanoids. There's no reason to believe that Pluto doesn't have them; indeed, it would be surprising if the dwarf planet turned out to be as smooth as a cue ball. But nobody has ever actually seen a Plutonian pockmark.