Wednesday Boy
The Nerd WhoFell to Earth
The problem with a Ghost is that they are by nature insubstantial or at least have phasing. That's a bit powerful to give right off the bat, but doesn't make sense why they wouldn't get it at 1st level. It's the nature of being a ghost. It'd be weird to be a ghost but be locked into a solid shape so enemies can damage you, yes?
Although I do think it'd be so easy to do a Werewolf class.
I can see where you're coming from because not having permanent phasing departs from the traditional image of ghosts and having permanent phasing would give the character a lot of room for circumventing many mundane challenges. (I don't think insubstantial is as much of a concern since it doesn't have a cinematic effect. It just translates to having extra staying power.)
But I think there's room to balancing the two so the character feels like a ghost while not being overly powerful. Since I can accept that a vampire doesn't get to turn into mist (Gaseous Form) until 10th level for balance reasons, it's not difficult for me to concede that a ghost class shouldn't get permanent phasing early either (regardless of how much I would want it). I can understand how it is a strike against the concept and potentially enough of a departure from the iconic image of a ghost to dissuade WotC from attempting to make it a class.
The element that I think a ghost class has over a werewolf class is that there are a number of iconic ghostly themes that could lend themselves to interesting and varied suite of powers: spooking, invisibility, phasing, death touch, poltergeisting, etc. Werewolves, on the other hand, don't have much going for them besides animal form, human form, and hybrid form. I don't see much room to develop a unique class from those elements that couldn't be covered with a theme (like the Pack Outcast from Neverwinter CG) or bloodline feats (like the Vampire Heritage feats).
But I'm not a creative game developer (although I am slowly trying to put together a ghost class of my own) and the WotC folks are. It would not surprise me at all if they developed an ghost or werewolf class that I found interesting and enjoyable to play!