I know that the majority of Mass Effect players were male (or there were A LOT of women playing as MaleShep) from BioWare's own statistics on it.
I don't think solid conclusions can be drawn from this, because:
1. Only 18% of those who finished ME3, at the time those stats were compiled, played as female. There is no word on how many picked up the game, played as femshep, and did not finish it (at least not before those stats were compiled).
2. Many women do choose to play as male, even when female is an option, just as many men choose to play as female.
3. As many of us have been saying, the lack of awareness of Femshep's existance meant that many women only picked up the game after they learned about her through word of mouth. I, for example, am not among that 18%, because I only decided to try ME after so many female friends recommended it. I thought it was just a regular shooter game, which is not something that is typically female friendly at all.
Your argument is basically cyclical. We should not market to female gamers because female gamers do not play the games that are not marketed towards them. We should only market to them after they have proven that they will play the games without any marketing towards them.