I recently did an analysis of Harvard and MIT's MOOCs to determine which gender gets the better grades in classes. (full post: http://minimaxir.com/2014/07/online-class-charts/ ) Turns out, there's no statistically significant difference between male and female grades. http://minimaxir.com/img/online-class-charts/gender-grade.pn...
Basically your post confirms the theory of the person above. That grades aren't measuring mastery of knowledge but the skill to obey arbitrary rules.