Some of them have relatively big legs and they most certainly aren't on bodybuilding dosages of PEDs so why not? Legs respond well to endurance reps in the gym as well so I can certainly see it building some size or at least not losing size.
I have no clue about their drug usage and have no opinion, not experienced or knowledgeable
on the subject.
The Tour de France riders (I know one, he lives and trains near me, used to fly past me when I
was out riding . . . he would draft his wife on her Vespa) or riders of that caliber usually, but not
always, have 'skinny' but muscular legs. And their upper body is nothing but a support system
for their legs. They are stick men on top as that extra body weight is just more to haul along.
Now the velodrome racers are sprinters and have way way better legs. (We have already seen an
example of that, talked that one to death . . . ) I have been to two of the Amgen's Tour of
California, been in the pits with the racers, now I wish I would have photographed their legs . . .
without being called a pervert.