I thought the "Games for Girls" vs "Games for Boys" slide today was interesting because it sums up pretty accurately the amount of thought that goes into designing for gendered audiences. I was an intern with a company that designs children's toys last summer, and it seemed that with each new design proposed there was the inevitable question, "Is this a girl or a boy toy?" followed by "We need to design a girl/boy version too." Typically what followed were some quick cosmetic changes (switch out the blues for pinks) and then we had two toy designs we could submit for the price of one.
I think that a lot of the reasoning for this gendering is based on marketing to parents, and not based on actual desires from the kids. After all, the parents are typically the ones purchasing the toys. It is easier both from a design perspective and a marketing perspective to simplify genders into binary categories, rather than to try to take in subtleties of actual desired play.