I'll pile on to the consensus. Force armor simply makes a wizard much sturdier than a DH. WD have spirit vessel, and of course monks and barbs have innate 30% damage reduction and tons of staying alive/mitigation tools. My wizard has 7k armor without a shield. A DH probably couldn't even hit that number with a shield - and then of course there's the force armor effect on top of that.
I'm not sure why kripp's wizard partner thought he might get one-shot. With force armor diablo couldn't even get close to one-shotting me on my wizard, not before 1.03, and not after. (I don't think they changed the fight any)
He might be talking about the DoT. That cuts around force armor and can take quite a bit out of you if you don't have much fire resist. With typical hardcore defensive stat stacking I can't see it being a real problem though.