In the published materials (as opposed to what happens around the table), it's primarily in the artwork, although some of the setting/monster elements also exhibit it.
I figured where you'd go first would not be where I'd go. I won't quibble with your assessment, but its not what I was thinking about. Where I would go would be:
1) The general priviledging of physical combat as the means of conflict resolution seen in many if not most RPGs, signifying the supremacy of martial virtue and its close association with male virtue over other sorts of virtues. And in general, the strong reluctance by many DMs to allow conflicts to be resolved in any other way. For example, many DMs just by fiat don't allow diplomacy, divination, subterfuge or even evasion. Or if they do allow it, they penalize it in some fashion, such as talking your way past a monster yields no XP and fewer tangible rewards in the form of treasure (loot being a traditionally martial reward). The only way gauranteed to work is force of arms.
2) In D&D in particular and in many games generally, the priviledging of strength as the primary and easiest means of obtaining combat supremacy and imposing your will on the enemy. In D&D this is generally the result of the hit point mechanic and the lack of an active defence mechanism, so that the battle tends to go to the combatant doing the most damage and wearing the heaviest armor. This system is largely unrealistic, and its unrealistic precisely in that requires a woman to be manly in order to compete on the one field of conflict the game primarily cares about - war. Moreover, probably this is one of the major reasons that Fantasy games, with their emphasis on melee combat, are far more popular than games in any other more modern genera. It's only in melee combat that a man's dominance of size and upperbody strength gives a truly considerable advantage over women. With firearms, women either are or are nearly the equal of men, and the same is generally true of 'push button' warfare. While there is a small gap between the best male FPS players and the best female players, the gap is not nearly so huge as between male and female melee combatants and the gap is far easier to close with far fewer biological limitations.
If D&D didn't priviledge 'maleness' so much already, it would be far easier to impose gender differences without it being seen as describing women as being inferior. But because we generally assumed the superiority of maleness for the purpose of the game, any attempt to impose physical differences on the two results in huge disparities in capability that aren't generally seen in the real world.
This priviledging of maleness in the game is seen in things like the half-orc racial template. It's an negatively unbalanced stat template on a creature that gets virtually no racial advantages, but its ok, because strength is considered by the game to be better than intelligence or charisma (or apparantly than intelligence and charisma combined).
If your desire for realism is so strong that you feel that you must encode such statistically-minor differences into your game world, then why stop there? Next up is presumably halfling strength modifiers, which are absurd. And then the next thing - bow ranges indoors, perhaps? And the next, and the next, and the next...
Why not? I've encoded harsher penalties for weighing 40lbs than exist in the RAW. I've changed missile weapon ranges. And the next and the next and the next. I'm probably already way further along towards a ruleset that encorporates elements of realism than you are going to get by brainstorming. How do you know that all these things don't also bother the person who wants to encode gender differences?
Curiously, we don't see repeated threads about hardnesses of materials.
Sure we do. I've seen them several times back when the house rules forum was its own forum. I was rather surprised to see this particular topic reoccur so soon, but I wouldn't have at all been surprised to see another variation of: "What's the realistic hardness of bronze, and iron weapons?" or "How can I keep the players from tunneling through stone with a magic sword/their bare hands at a high rate of speed?"
