Q: Why does my 15-inch Macbook Pro identify its self incorrectly?

I recently got a 15-inch Macbook Pro 15-inch and it seems to be identifying its self as a Macbook 13-inch. I'm not quite sure why, but the model identifier is MacBookPro9,1. Looking on the Identification Page - http://support.apple.com/kb/HT4132, it seems that it should be identifying its self as MacBookPro9,2. Is this normal that it identifies its self incorrectly? If so, whats the reasoning?