I know what they're playing: Farmville and a bunch of HOGs (Hidden Object Games). Most of that 40%, I assume, would be casual players. The rest (much smaller percentage) would be hard-core gamers who play more advanced and more variety of games across multiple platforms.

Regarding the OP, I would start off with gender neutral games that are easy to pick up like Mario Kart, Sims, Katamari Damacy, any casual game, and so on. I got one sister to play because she was watching me play Chrono Trigger years ago. She's played other games since then. I think just as long as it looks interesting, fun, or if the story is good, then you can entice them to try it out.