Circumventing the rules is pretty much seen as just another avenue of development and if that includes monkeying with the riders themselves so be it. You hear major protestations from teams and organisers about stamping it out but the fact remains that unless someone is caught in the act then transgressions are only discovered after the fact. After all, once you've been photographed on the top step of the podium with your sponsors name across your chest whatever goes on a few months down the line is pretty much immaterial. Add to that the fact that most anti-doping measures are testing for procedures that are years old and you have a self repeating cycle of scandals.
My favourite ever story is from the Tour during the 20's I think (I'd have to dig out some books at home to give the specifics) but it involved a couple of riders who would, during some of the flat boring stages early in the race, ride some distance clear of the field until they found a likely village with a cafe. They'd wait for the Peloton to arrive (passing the time with a bottle of the local red) and throw bread rolls at the other cyclists as they passed. Spontaneity is one thing that amateur sport will always do better than at than the more organised and professional events, which is a shame really as it gives the competitors far more character.