These athletes must not be as serious as you think. Smoking, among a laundry list of other adverse effects, will decrease your lung's capacity to get oxygen to your blood. So any truely serious athlete would never smoke, knowing that it can have a large negative impact on their performance.
I feel its necessary to point out to everyone that even "casual" smoking (once a day or a couple times a week) is only slightly less detrimental than chain smoking. Don't kid yourselves, anytime you smoke, you are harming not only your lungs, but you heart, blood vessels, and every other organ in your body.
It takes around 5yrs of non-smoking to return to the same general mortality rate as non-smokers.
Sorry, just learned too much in school to understand why some people still smoke.