From what I've seen in his speeches etc, he strikes me as a very intuitive artist and by his own admission he tries to avoid too much research because it delays or interrupts his writing process (From A Buick 8 and 11/22/63 being obvious exceptions that spring to mind). I have noticed the frequency of the protagonist being a writer in his novels, but I've always accepted the fact that he is using what he is comfortable with/knowledgeable about as a launchpad for his ideas. Off the top of my head, in his stories it is rare that the character being 'a writer' is a vital characteristic that the story arc depends upon - more often than not it is just used as a starting point to deepen the backstory, create a setting, etc.