Basically if a young player has the skills and smarts to play in the NBA their progression nearly always comes down to having a comfort level on the court! I really think this is true at all levels of BB. That's generally why you see young guys on BAD teams progressing faster than young guys on elite teams (such as the C's)! Coach's like Doc can't afford having these guys make mistakes, costing games when trying for a title, whereas the bad teams can let them play through the mistakes and get a quicker, true idea of whether or not they'll cut it some day.
For that reason again, guys in the D-league relax and give a truer indication of what their game might really look like if given the chance to play without worrying about being yanked out of the game with every turnover, missed defensive rotation, or missed shot!
Until guys like JR and Walker truly get those kind of minutes it is really hard to tell how they'll turn out, IMHO.