Image from here.
Bradley Wiggins, team captain of Team Sky, will end his pro season in September with the Tour of Britain. For most riders the Tour de France is the last race in the pro tour season save for a few crits here and there. Wiggo is keeping his form straight into fall. When most riders will be vacationing, he'll be training. There are pros and cons of extending an already grueling season. One major con is the physical toll on your body. Trust me, after ALC9 I did no physical activity for 1 week. Just imagine doing ALC9 every few weeks with a training rides in between. One pro is you keep your riding form. Less down time is less time needed for training.
I believe that cyclist are one of the best endurance athletes, with top honors going to ultra runners.