AbdulAlhazred
Legend
But my response is that level limits for demi-humans in D&D/AD&D DO serve a design purpose! They act as a disincentive to play as a demi-human, which is otherwise in most cases a mechanically superior option. The designer of the game, Gygax, was not interested in a game which depicted bands of superior demi-human adventurers lording it over the human 'normals'. That simply wasn't the milieu/genre he was interested in producing, and thus he introduced mechanical constraints designed to make that outcome unlikely. My point being, there never was any sort of viable simulationist argument here, the rule is PURELY gamist, or at most could be seen as being part of a 'high concept' in which the genre is meant to be close to that of most S&S from which he drew inspiration, where humans are the only/main protagonists (even Lord of the Rings is MOSTLY about humans in an overall sense, despite the main characters often being 'demi-human').To elaborate on the "as if"... It was common back in the day, and still is in some corners of the OSR world, to explain some of the more bizarre design decisions of early D&D in terms of "realism".
For example, level limits for demihumans were explained by, "If they could keep levelling over their long lives, they'd dominate the world!" Which, it is explicitly or implicitly stated, would be "unrealistic".
Of course the retort is perfectly possible (and was made even in the early days) that adventurers are extraordinary people who don't necessarily match the broad demographic profiles of the population... And that in any case, why do game mechanics have to support that degree of world-level "realism"? But that retort had remarkably little effect.
I suspect that anyone who insisted on level limits would, if pressed, admit that they don't really think population dynamics can or should be embodied in game mechanics. It's just too complicated a subject even when restricted to humans! But they want to feel "as if" that embodiment had been done. It makes the world seem more alive to them, more independent of their individual game or convenience.
(Naturally, not all sim players cotton to level limits, I'm not claiming they do. I'm just pointing out a dynamic that seems to me to be in play for those that do.)
I am certainly willing to agree that if a game designer can construct their system in such a way that a significant segment of the gaming public is able to reason about it in 'simulationist' terms, and that makes them satisfied with the result, then the resulting game is probably going to be better received. In terms of the actual topic of the thread, I think this is a point which is likely to be important to someone including 'plot armor' of some sort into their design, or 'mook rules' like the 4e minion rule.