Since we're typing the famous ones, it applies to them and not starving artists. I think NJ's are more likely to see the big picture of what they want to accomplish, set the end goal for themselves of how they want to get there, and then throw themselves out there to get it.
For example, an SP friend and I both want to be novelists. She writes occasionally--"when inspired"--and can never seem to finish a book. She doesn't stay on the same project for long enough to do so. Her writing is pretty, as she focuses on finding the perfect words to describe the surroundings of her characters, but she told me she has trouble finding the big picture of her story.
I set a goal to write a book with the specific idea of what I wanted it to be, set an amount I had to write a day, and started on my goal. In less than a year I had an edited book and a credible literary agent. (I'm still waiting to hear back from publishers!)
But anyway, the point. NJ's are more likely to focus on that end goal of publication and learning everything they can do to achieve it, whereas SP's are more interested in the process of getting there. Of course this isn't a given with everyone -- there are successful SP writers -- but it could be a starting point.
And I'm still sticking with my theory that because there are more N writers, they are more likely to create N characters
