I cannot say much about gaming purchases as I am not a nerd.
However you seem to be assuming that gamers purchase the games they play. While this me be true for a good portion of them, a very large number of people (myself included) just download shit. The smartest girl I know is an average reader. She's not wealthy and has very little money to spend on anything outside life's basic necessities. Most of the books she reads are, as a result, downloaded copies of e-books. And back when I was young and played some games, I would always ask technically savvy relatives or friends to download them for me.
There may be a lot of female gamers who game all the time, but never purchase the games they play. No statistics would cover them. This goes for several things in life. One might assume a certain group of people reads little, since they purchase few books the same way one would make such assumptions on a certain groups gaming habits. But it doesn't necessarily have to say anything.