(Usual disclaimer about these only being generalizations and there are many exceptions, blah blah blah)
This topic evolved from a conversation with a woman in my gaming group, who obviously games, and with my wife, who doesn't. The gamer girl population increases every year. In many avenues, females can actually outnumber males. While this is good news, the bad news is how little this is actually changing the games themselves. At a BlizzCon panel discussion an female querist was booed for suggesting that maybe the female characters should be able to wear clothes.
But the problem goes way deeper than that. Even within RPGs where female gamers are not only accepted but delightfully encouraged, the roles they prefer are often within healer, support, or diplomatic archetypes (again, major generalization, but largely true nonetheless). Wish fulfillment seems to be the more desired form of escapism as opposed to power fantasy or strategic simulation.
Tabletop gaming's roots are wargames, and this continues to form the foundations of almost all mainstream RPGs. The point is ultimately combat, no matter how many peripheral rules and options exist within the particular game system. And at the end of the day, many women just aren't interesting in killing things and taking their stuff.
Assuming you accept my premise (and I know that's a big if), this should be informing game design, but it isn't. With the notable exception of Nobilis, even games with female contributors ultimately seem to be about fighting. Beyond the wargame roots, the other obvious explanation is that combat is the most easy and obvious form of conflict, and it's hard to build any kind of play that doesn't revolve around conflict.
The video game world started to figure this out, and we got the Sims, a fantastic series of games (It is; deal with it) that is also more popular than the Bible. A Second Life is still in existence, largely due to its popularity among female gamers.
I also believe the popularity of Game of Thrones lies in its evolution from the Tokienesque war of good vs. evil toward a focus on individual characters striving toward deeply personal goals.
The question is this: If the bedrock of tabletop RPGs were not male-centric wargames, but rather a different female-centric or androgynous premise, how would it look different? How should this change in thinking change the way we're designing games?