Here's a guess: Women, on the average, are older than men. So women, on the average, have fewer teeth.

Sounds logical. But, and I'm not sure if it's correlated with gender, my mother and her mother both have several baby teeth with permanent teeth above them still, so there are cases like that screwing with the data.

On a related note, Google Image search for "baby skull teeth" is quite interesting.

Fewer teeth in their mouths .. don't go there if you're squeamish.