1. He's fan favourite.
2. After that Illidan stunt, noone stays dead forever.
Considering that the Forsaken are unable to have any facial hair, it might have something to do with the fact that he was just a well-preserved undead. That said, it'd be cool to see Forsaken sporting moustache they scalped from some unfortunate gnome.
It's like Joe Dirt.......you know how Joe was so ingrained white trash that his beard just grew in that way.....same thing here. He was just always sporting the "cool guy stubble".
Me thinks Chromie has a whole lot of splaining to do!