Girls bring drama, plain and simple. The only multiplayer games I play are MMOs and I've encountered many female gamers and have been in raiding guilds with many. Out of all the girl gamers I raided with, I can honestly say only two were truly great players, and even one of those two brought relationship drama with her.
A good portion of the girl gamers I've met were in leadership positions in guilds, either as the GM or a GM's girlfriend/wife and it's never ended well for the guild.
As for the study, it's "accurate" if you count mobile games at the same level as core gaming. It still doesn't mean that women are an important demographic in strategy gaming or FPS for example.