I wouldn't go that far as to say half of the gamers will be women. It's still dominated by boys and men, but yes it is increasing as far as the number of female gamers that are playing now. I know a number of them that are really good too.
I think there are a lot more female gamers than many think but I don't think they make up half the gamers out there, unfortunately. I think video game developers know it. I think if more women played we could send a message to video game developers to make games that aren't sexist.