I'll try to dig up a link.
It seems that the more exercise you get, the more oxygenated your gums are, and (gum disease) germs survive better the less oxygen there is- so marathon runners have an extremely low incidence rate of gum disease! wow.
I'm theorizing that cyclists are somehow protected by constant movement (unlike surfers waiting for a wave). Perhaps the airflow is protective? Or perhaps it makes cyclists aerobically fitter, and this makes their skin more resistant to sunburn (and therefore skin cancer).
Some cyclists do use long-sleeve summer jerseys, but they're in the minority. Short sleeve and sleeveless jerseys are more popular because they are cooler.
I fried myself once when I was sailing, and I had the worst burns on the bottom parts of my body (bottom of chin, bottom of knees, basically anywhere the rays hit me after bouncing off the water.)