The structure of the competitions is rather different. The Grand Tours, the very longest thing is cycling, is only 3 weeks. Then the historical scoring in those Tours is setup with the idea that riders may exit the Tour. Forget drugs, they leave because of illness, crash or simply not wanting to deal with the mountians for sprinters. A team leaving a tour hurts but does not kill the competition. But in head to head team season long competitions what happens with games already played? Are they thrown out? Real problem as what is done to the team of the doper has the potential for a huge impact on which non-doping team wins the season.

Personally I like the way it is working in hte TDF right now. Teams where a member is caught seem to withdraw. This may be the best if it can become an expected reaction. It leaves it open so teams can stay, so a minor member really going against team policy won't cause a team to unjustly be thrown out.

I am convinced that at this point teams withdrawing are doing so with the blessing and perhaps even active encouragement of the Tour itself.