In general, a health bar exists as a progression tool.
As your character becomes stronger, it takes less hits to kill weaker enemies. In zelda currently, it's the same amount of hits to kill the first mob as it is to kill something else, within reason.
So yes, as you progress, it should mean that every enemy takes the same amount of effort to beat, but as you return to previous areas, those other enemies will become weaker.
In the original, this was somewhat made clear by having two different colors of enemies. Red immediately came across as tougher, and they obviously were as soon as you fought them, so you knew that was a difficult area and probably not one on your current agenda.
But health bars are a little more elegant, as you can have grades of tougher enemies without having to repeat enemies with color variations.
I think this is a great thread, spemanig. Great observation.
