AbdulAlhazred
Legend
The bit of that rabbit hole that I ignored was the completely unsubstantiated assertion that the meaning of "realism" in RPGing has changed in the past 40 years. Obviously I missed that memo (despite playing Rolemaster continuously from early 1990 to late 2008!).
That is one [em]huge[/em] rabbit hole. I think it is more like a dragon's den! Who wants to march into that thing??!
I was a wargamer before I was an RPG gamer. I don't think there is a different definition of realistic. There may be some differences in the two genre of game, not surprisingly, but the same considerations faced Gygax in designing D&D as faced Gygax in designing Chain Mail. In either case you need relatively succinct mechanics which can provide a range of outcomes which would occur in the thing you are simulating.
In the case of Chain Mail, the designer probably hoped that the mechanics of combat also produced results which were reasonably true to life. If a Roman cohort in good order stood on an even piece of ground facing off against some Celtic irregular warriors, guess what would happen about 99.9% of the time? You can produce this sort of outcome pretty reasonably in Chain Mail, and it can be run in a fair amount of time.
Note, however, that Chain Mail does recommend (I don't think they demand it as a necessity) that there be a referee, who would likely adjudicate things not explicitly covered in the rules (IE decide what the effects of heavy rain might be on some archers).
D&D obviously evolved from this, as we know, but the areas which it covers are much more diverse and this is probably why Gygax puts 'realism' in quotes when talking about D&D. Not because he is using a different definition, but because he simply has different goals and depicting heroic fantasy adventure doesn't need to be realistic in the same way that Chain Mail does.