So I read the column on female athletes and bust size and was surprised on the amount of biology missing.
I recently graduated from college with a science degree. It was discussed numerous times the likely cause of this phenomenon.
There is a hormone called leptin produced in the body that has to do with appetite. Its concentration is directly correlated to the amount of fat in the body. When a female athlete trains hard, such as for marathons, her body fat decreases to the point where leptin concentrations are unusually low. It is now believed that this decrease triggers a hormonal response that stops her from menstruating (the reasoning behind this being that her body does not have the energy to support a pregnancy).
This hormonal effect in itself may help explain to some extent how endurance female athletes tend to have smaller chests. In addition to this, if a female athelete starts training early, such as olympiads, they may actually have never entered puberty. You may wonder why many of our Olympic female gymnasts have such high voices and small bodies. Once these athletes ease their training or stop altogether, they enter puberty (finally).
I believe it is these factors that tend to cause female athletes to be smaller in the bust area, in addition to the selection process that weeds out women with larger breasts due to discomfort.
From the column:
Or is this another instance of information added after the fact? 
The reason I overlooked that is because the next paragraph read:
“…breasts are 80 percent glandular tissue and only 20 percent fat. They claim their studies show there is no statistical correlation between body fat and breast size.”
It seemed that Cecil was saying that the body fat/breast-size correlation was due to a loss of fat in the breasts, not due to hormones, and that some doctors contradicted this by saying that the breasts are only 20% fat. I was trying to show that there are more factors at play than just fat, particularly hormones.
Looks to me like the Master’s answer was dead on. The biggest (no pun intended) reason clearly is that large tits jiggling around will cause painful abrasions. This will mean that self-selection will get rid of almost all well endowed women who are athletically talented. They’ll just do something else with their life rather than try and become an Olympic athlete. Note also there isn’t much potential for a big breasted track and field athlete to make good money in pro sports. Thus why put up with the pain if there is no payoff?
Yes, Cecil was right on that explanation, but he is usually more thorough than that and explores various possibilities rather than just settling for one. He only briefly skimmed over the other possibilities.
In class, or in the bleachers?
(I keed, I keed.)
While your explanation might hold with female gymnasts, who peak out at like 13 or so, it can’t hold weight too terribly much with female runners, softball players, basketball players, etc, since in these sports you usually only start at age 13. (Unless of course you’re Kenyon, Moroccan, or from some of the other African Nations, but the small breastedness is a worldwide phenomenon.) The hindrance of hormones wouldn’t cause large breasts to reduce, it would only cause them to not develop in the first place.