Arthur Tealeaf said:... imagine how a person would look after 30 slashes from a greatsword--and remember that each and every of those slashes would probably kill a commoner outright (okay, mortally wound)...
Lets imagine how any human would look after just ONE solid hit from a greatsword. Picture it. Gaping wound. Gushing blood. Traumatic shock setting in. You get the idea.
Can you imagine anyone surviving such a wound without aid? Can you imagine anyone surviving thirty such wounds?
I can't, that's why I look at Hps as the ability to AVOID a solid hit. A high level fighter/barbarian/whatever doesn't just grit his death & refuse to die (well, maybe a barbarian does while he's raging, but that's another topic). He hurls himself aside just far enough to avoid the worst of the blows that would otherwise bypass his defences and strike home.
Naturally, there's only so many times one can keep dodging well aimed blows, so you keep losing Hps until finally a blow does strike home and you suffer a life threatening wound. A wound that likely WILL kill you unless treated. A wound that drops you into negative Hps.
Looking at it this way just seems to make more sense to me.