As a basketball fan, I love this kind of analysis. As mentioned in the article, I think the defensive skill of NBA players is a big reason for the differences in accuracy within six feet. For many NBA players, it's much easier to take a 7-12 foot shot than to challenge the taller/stronger players that defend closer to the rim. On average, the "rim defenders" in college aren't as strong, making it easier to score on dunks and lay-ups.