Anybody who still thinks leg shaving has anyting to do with aerodynamics or hygiene simply hasn't understood the psychology of the pro rider. Leg shaving is the rite of passage that signifies the entry into the professional world; as Matt Seaton writes in his excellent book The Escape Artist, a cyclist with unshaved legs would be laughed out of the peloton. It's all about purity and asceticism and the look. The most likely practical reason is for massage, where long hairs tug painfully and make life hard for the masseur.