So that class with Karl Gnass pretty much just payed for itself last class when he offered many of his theories about why people draw the way they do- this particular once concerned head placement. I'm probably butchering his words, but: "a lot of times artists will start learning about the human body with the head. They'll draw the head many times over and so when it comes down to drawing the figure they'll overlook it cause they think they know it."
His words were way more colorful, so if you're in the area- take the class! so good!