You know, I was really hostile to that when I first saw it; I came from a background of a number of games like RuneQuest and Fantasy Hero where opponents were fundamentally not built any different than PCs (other than the obvious matter of degree in some places).
But D&D, particularly post-3e D&D had too many moving parts to make that possible, especially as you got to advanced opponents for representing them all in the same detail to go well (I saw that at the end of the 3e campaign I ran), and trying to still capture some of the more exotic things required some corner cutting.
I don't still particularly like it, but I understand the virtual necessity.