The Vitality formula isn't entirely correct, only I'm not sure why. I don't know if it changes after a certain Vitality threshold, character level, or difficulty level, but my Demon Hunter in Act III of Nightmare gets 20 life per Vitality. I know it used to be 10, so I'll have to do a little testing to see when it changes. Perhaps you gain 10 Life per Vitality in Normal, 20 in Nightmare, 30 in Hell, and 40 in Inferno?
Roland *The Gunslinger*