[Anaraxes]

On the other hand, source fiction has plenty of examples of heroes that take a beating, and keep on going, gradually getting worn down.

I was struck back when I saw Taken, with Liam Neeson, for example. It seemed like a classic D&D dungeon to me. In one early fight scene, he starts a fight in a tiny interrogation room with half a dozen mooks. Sure, they're in arm's reach -- but in a realistic game, there's no way he wouldn't have been dead on the floor. All it would take would be one of them (even if he's the last of six) to pull a trigger. But, our hero takes them all out, because they're mooks. But he does get a little beaten up. There are a few more encounters, leaving him more tired and bedraggled looking after each, which of course just serves to make the final boss fight that much more dramatic. That progression would be well modelled by wearing away an ablative hit point resource, hoping not to run out before you finish the dungeon.