I was confused by this too... i mean, it makes sense for swimmers to shave just about everything, because i know hair makes a huge diference on water resistence (literally seconds), but wind resistence in cycling? hmm....
one of the guys on the cycling team here said it's to prevent infections in the case of a nasty fall. apparently guy- hair is thicker and harder to clean out of cuts than girl-hair, and gets all itchy in the bandages (not to mention the pain of ripping a band aid off your hairy leg- ouch!). if a guy wipes out and gashes up his leg it's more likely to get infected if he didn't shave (nice visual there, eh?)
this is just what i've been told... maybe it is just for looks... after all, it's MUCH harder to see the muscle definition on a hairy leg than on a smooth one