IMO It is because women aren't as aggressive as men(naturally).
Our 'chess play' directly reflects our personalities, and our character. I've noticed MOST women play VERY defensively. While 'this style of play' can do just fine in chess, if you look at the best players ever, they ALL go straight for the jugular EVERY time(an instinct that mostly only 'the hunter' has).
I have to disagree with you...women are just as intelligent as men and..to be quite honest moreso...there just are not enough women playing chess compared to men...they have the advantage of distraction when she is attractive and shows cleavage...it all involves on focus and strategy...