It's a cultural thing. In group rides, seasoned cyclists supposedly trust ones who have shaved legs to ride with them over those who don't. It suggests you have a better idea of how to ride in a peloton than one with hair who might have just come off the street and join the group.
There also is the crash factor to consider and how less hair means less loss of flesh and later, less tearing when the bandages need changing.
Shaving: I've done it, and thinking of doing it now. Some chicks dig it, others will think you're queer. So what, who cares.
2 mph faster? Highly doubtful. A 22-pound Torelli is quite a load that I don't believe shaved legs will make much of a difference on. It didn't on my 22-pound Colnago back in the day when I shaved.
Though you do see better muscle definition.
