Such a rule is not Gygaxian realism, it's not simulationist. It's part of the 4E narrativism that turns off a lot of 3E players.
I think what is meant is "Gygaxian Naturalism". According to its proponents, this is theGygaxian...realism?
tendency, present in the OD&D rules and reaching its fullest flower in AD&D, to go beyond describing monsters purely as opponents/obstacles for the player characters by giving game mechanics that serve little purpose other than to ground those monsters in the campaign world.
The purpose of this is said to be
to paint a picture of a "real" world, which is to say, a world that exists for reasons other than purely gaming ones. The implication is that monsters have lives of their own and thus go about their business doing various things until they encounter the player characters.
(I think the original blogger of the notion somewhat contradicts this claim about purpose by going on to say this is
one reason why AD&D has stats for so many kinds of "ordinary" animals: you can't build a "real" world without stats for sheep and cows and horses and such, because you never know when the PCs might need to kill one.
This doesn't sound like part of a program of statting things up independently of their mechanical interaction with the PCs.)
Anyway, whatever the general status of the notion, I think it has one particular implication when applied to hit points (not a logical implication, but at least an implication of tendency): it implies that, at least as far as monsters and NPCs are concerned, hit points are meat. Because, to the extent that hit points are not just meat but also luck, divine favour etc, it does not contradict the notion of a PC-independent gameworld to posit a skilled, well-trained (and therefore high level) monster or NPC who is simply devoid of luck or divine favour, and therefore apt to be killed by a single sword blow (as tends to be the case for even the most skilled non-protagonists in REH's Conan, for example) - and this is exactly what the typical 4e minion is.
This much at least is true! (And once again we see that it all boils down to hit points, and different understandings of how these correlate to the ingame reality.)This is one of the game splits that D&D 5 will have to deal with.