What he said sounded strangely sensible.. but maybe I'm crazy. But it seems true!
Sure, it makes sense, but males have more muscle by nature. Plus, I don't think the average breast size would cause any real problem.
On average, men are more competitive in sports (running, basketball, football, etc).
Muscle can help a man (or woman) propel themselves through the water with more force. If breasts don't cause at least small problems, then that would seem kind of strange considering the fact that small body hairs do, since swimmers shave themselves. I'm pretty sure that breasts can help slow down a woman in the water. When a woman is swimming in the water, her breasts will be down more, thus causing at least a small bit of drag. Like I said, muscle is not always bad in swimming unless the person has very bulky muscles. But toned muscles will only help (by lifting weights at lower weight and with a higher amount of reps in each set, muscles don't get bulky, but become toned and strong), as they allow more force in each stroke... the force mixed with less drag on the body will allow one to move much faster through water.
Joe, what you said about testicles seems pretty stupid to me. Your testicles only turn blue if you are in water that is cold enough to cause hypothermia... otherwise your balls just shrink temporarily. And if your balls shrink, then obviously that's better. Plus, balls are much smaller than tits (ok, maybe not always!). Your balls, while swimming, are going to be in line with the rest of your body, and won't produce drag. Your dick, if you are erect, will cause drag. Maybe men are slower when they are being beaten by a female in a race, because they are busy looking at the woman in front of him, and he gets a boner and the erect penis causes drag. I'd say that is a good Joe[x86]-like theory.