Sherlock Holmes: 60 for 60

I suppose the main problem is that ACD's characterisation is not always consistent ^^ But you've answered your own question: Watson probably emphasises Holmes' otherness to make him seem a more exotic hero for the stories. When you look at it, the truth is rather mundane - Holmes isn't really a superman; he's a highly intelligent, contentedly unsociable man, who works hard to develop his skills.