When I was younger I felt that a lot of roleplaying games underestimated the lethality of weapons. From swords to guns, you should pretty much be dead after you're struck, thought I.
It was only as I got older that I realized the opposite was true. Certainly, if your head was cleft from your shoulders or your brainpain annihilated you would be dead. However, as I became more and more knowledgeable about history I began to see the cases in which grievous bodily harm didn't result in death.
Henry V was shot in the face with an arrow and survived. There have been many carabinieri and condotta that were shot with lead balls and survived to tell the story. In one of the classes I took in medieval studies (Rome and the Barbarians, with Prof. Robin Fleming) we looked over a lot of human remains... remains that displayed healed sword-cuts, broken bones that had been set and other such wounds that failed to slay their target.
So as I looked over HP and waded once again into the complex HP debate I realized that I actually liked HP even more than I thought. It's flexible, represents real and lasting harm done to the character (meaning a blow, even if it lands, that does little more than bruise is probably not HP damage) and also accurately depicts the moment of a debilitating strike: ie, most warriors don't get worn down in combat, grow sword-weary and sluggish, and then fall; rather, it is more likely that they will sustain minor injury until at last their guard is down and the stroke which drops them is delivered.