Boris was able to heal three deep lacerations in only a few hours when he was first infected. When transformed he can heal that much in mere moments. Werewolves are nearly impossible to kill without silver or enchanted weapons (speaking of which cough cough, http://borisandbjorn.thecomicseries.com/blogarchive/19830 )
Thanks. I admit that the healing factor is a bit overused, more so in superhero comics than in the fantasy genre, but I thought it fit well with the properties of a werewolf, what with them drastically and rapidly changing their body structures when they transform. Plus, now I don't have to take it easy on him. There's a lot of trouble down the road for Boris.
Well, it's often necessary just for plot purposes. You can't have heroes lying in traction for weeks and months, or falling apart from old injuries-- especially not in longer series where they have to survive and stay mobile. Even the more realistic Daredevil show on Netflix gave Matt a super-healing meditation technique.
http://borisandbjorn.thecomicseries.com/comics/51/