I'd say that "technical" sci-fi, focusing on technologies and science rather than on interactions between people (large parts of Star Trek, for example), tends to fall into the "male" category of thought; remember that, in our current patriarchal soceity, most females are enocouraged from a young age to develop more "people" skills while males are encouraged to develop more "technical" or agressive skills. So things such as Wargaming usually appeal far more to males than to females. Not that there are no exceptions, ofcourse, but the tendency of the later editions of Traveller towards the "wargame" direction, not to mention the focus on hard science as opposed to social interactions, repel alot of potential female players. I know several women who like to play "sims" (e-mail based, "freeform", story-heavy RPGs), especially in the Babylon 5 universe (which tends to have alot more female fans than StarTrek, probably due to the fact that this show focuses on alot of interpersonal and political interactions and very little on science (science is in the background, yes, but people/aliens are on the foreground).
Ofcourse, there ARE women who enjoy the allegedly "male" fields such as gearheading and grognardism, though society still discourages such behavious in women. Also, I think my mother would've easily become a wargamer if born into the right era, as she loves action films/TV series and thriller books, and was, as a child (in the 1950's), quite an avid player of "box games" (monopoly, checkers, and various games that are probably local Israeli inventions). Truth be told, she've introduced me to RPGing in a sense - she loved to play various imagination and storytelling games with me when I was a child, usually where I controlled a character and she've made up the environment/other characters (no rules, ofcourse, just freeform talking).
From my experience, women tend more to the direction of rule-light storytelling than towards wargaming.
Another problem I've encountered only seldomly but that I know of is the tendency of some of the younger RPGers (read: insecure and immature early-adolescent boys) to scare and/or mistreat women gamers due to sexist prejudice and/or inexperience in interpersonal matters. Contrary to pervailing stereotypes, most RPGers aren't like that, even at that age, but there ARE ones who acts just like the stereotype and they scare off alot of good potential female (and male!) gamers.
As for me, alot of my more recent Traveller materials (my lighter rules and the Celiran race, yo state two examples) were significantly influenced by discussions I had with my girlfriend; she has a magnificent imagination and a very sharp mind, not to mention applying her professional knowledge of biology to create logical and interesting imaginary lifeforms and interesting imaginary soceities. I think that once she'll get a good grasp of the rules (they intemidate her a bit, especially mathematical ones - she is still traumatized by college differential calculus) and of the distinction between a referee and a player, she'll make one great Traveller referee (as she has just the right kind of imagination
).