I've long considered this, since 2004 or so. They only appear in his realm, are very powerful and apparently old - some were frozen statues when the Nerevarine first appears. They never appear untransformed to my knowledge. They're very possible Hircine's elite Daedra servants, not much different from Sheogorath's Golden Saints, Dagon's Dremora or Meridia's Aurorans.
The werewolves named 'Hircine's Hounds' are considered purely creatures by the game, I think (can't remember for sure). They are separate from the wandering werewolves usually encountered, and yeah, they appear as Statues, something that I feel asks questions.
That isn't to discredit the idea that werewolves live longer lives- in fact, if its true, and they are Hircine's elite servants, then the fact that mortals emulate their form makes them half-daedra in a way (another thing I've been wondering) which would surely effect life expectancy.
I like speculating.
I would hang out here more often, but I have a phobia of lorists.