Three of the females from Firefly (and a case could be made for Kaylee) don't fit the "I'm crying and I need your penis" role. Inara had a ton w/o trying, River was more likely to kick one off your body than anything else, and Zoe was the penical owner in that relationship.

Can't comment on his other shows though. I've only seen parts of Buffy and Angel, and Dollhouse is still unfolding into something that seems to be more "I'm a guy and I think you need me, so I'm coming to save you whether you need it or not, but I will probably find out otherwise in the end." Worst sentence ever.