Ron Edwards:
"The description of Vitality should include some kind of general statement that the demon's Power is often used as an addition to the user's score for all sorts of reasons which involve resisting harm or strain. It's a Customization Issue." [1]

Vitality can, if designed correctly, be used on a Target/User; in other words, on someone other than the Sorcerer or Demon (just like most other Abilities, but somehow this one doesn't occur to people).