I think the problem here is that, truthfully, we do not actually know what dissuades women from STEM subjects. We make many a priori assumptions, usually from our own innate biases - so us hairy blokes say it's because women aren't apparently interested and the hairy feministas say it's because us blokes are so horrible. Truthfully we just don't know, we just have opinions.
Err, no. There has been much research in this area and the results are quite conclusive. Males are more interested in "things" than females, it's an evolutionary trait and is also found in other animal species. It's actually a really fascinating subject if you want to go down that path of investigation.
As the wikipedians say "[citation required]". I've never seen anything "quite conclusive" that can extract the signal from the noise. There's sex, genes, upbringing and socialisation all working to confound things. Add confirmation bias to that, in both researchers and readers of that research and I think we're quite a long way from "quite conclusive".
That a bunch of monkeys will segregate on sex lines in playing with human children's toys in the same way that humans do (I'm serious, they've really done this research and drawn conclusions from it, which is what I suspect Dave is alluding to in "in other animal species") is not particularly persuasive that there's a deep rooted biological bias in operation here - at best it's suggestive and that suggestion is that more research is required before forming any conclusions.
It's one thing to say, possibly even prove, broadly, that males are more interested in "things" than females, it's another to conclude that is the reason, and the sole reason that there are so few women in STEM subjects.