Your comparison is invalid, e.g. JK Rowling doesn't write books about how you should become a magician
There's more to this than meets the eye.
It depends on how you perceive writing. For example, "Old Man and the Sea" might be the greatest essay about criticism ever written, despite the fact that it's not an essay. You have to see through the story to get to the essay.
I think the reason so many people enjoy Paul Graham's writing is not only due to the subject or the genre, it's that he transcends the category, much like Hemingway did when he wrote "Old Man and the Sea."
For others who might be curious about the Hemmingway connection, http://petersencj14.blog.com/2013/02/15/an-essay/ seems to explain what you're referring to
Each of Paul Graham's essays were written as he slowly evolved into the man he is today. He was changing the entire time. Also, he knows more now than he did before.
The thing that saddens me is not Paul Graham getting advice from friends, it's people who try to take some of the shine off.