Having that much arm muscle is only neccessary for mt. biking. For a stage cyclist, every ounce of muscle they have that they actually don't need slows them down, tremendously. The tour de France ends with a 23 km climb, after 3 weeks of racing. On a climb like that, an extra pound could slow someone down by 30 seconds. Thats 30 seconds spread over an hour or even several hours, but nonetheless, significant.
Also, Lance has a rare condition that I have slight resemblences of. He is able to use more of the oxygen that he takes in. It came useful to him in cycling, for me it was wrestling.
Skatha, were you a nuclear medicine major? many of my friends in my school are studying the same stuff you just described.