The Wikipedia entry also provides a link to studies which explain why high performing math teams tend to have more males than females. Linky
The long and short of it is that while both boys and girls have similar average scores, the boys have a higher variance
than the girls. Meaning they have more very high scoring members of the population and also very low scorers. The girls scores were more clustered around the mean.
So if there was a team made up of the highest scoring math students there is a much higher chance it will be mostly boys. No penis driven oppression, no grand conspiracy, the teams are drawn from the best in the population. Though, if it makes people feel better they could form a team of the absolute worst math students and it would be mostly boys as well.