Imaculata
Hero
A related issue is that it uses things like "natural armour bonuses" to give a veneer of simulation to what are in fact features of the game driven purely by system maths (eg dragons have +30 "natural armour" bonuses to their ACs, but a +5 suit of plate armour ie the best that a mage can forge, gives +15 or so to AC - what does that "natural armour" actually consist in, not in system maths terms but in in-fiction terms?).
I see 4e as having made a clear call in this respect, and that's one thing I like about it.
As I understand it, natural armor is not only the material, but also the thickness of a creature's tough skin, as well as a way to balance its difficulty. But I don't think it was meant to give 'a veneer of simulation' at all. It's part of 3rd edition's armor mechanic, and that's it.
Why do you need to make an exact call about what it is? Does it change anything about the gameplay?