I just don't buy that 5 minutes of sporadic playing time as a Freshman really does much for a kid's basketball development beyond helping a kid's confidence stay up, and minimizing the chance of a transfer. Joel James has played pretty well. True. But so has Marshall Plumlee -- a guy who really didn't play a meaningful minute in his first 2 seasons. Ryan Kelly is in the NBA now, and was a very good college player his last 2 seasons. Ryan too hardly played as a true freshman on the 2010 national title squad. Grayson, last year, was in the witness protection program until Sheed got dismissed. And, yet, he continued to improve into a solid contributor last year, and a star player as a soph.
I don't have a problem with Roy playing more guys -- as it's something that is essential to ensuring that UNC can play at the pace it would like to play. However, I don't think a couple isolated minutes here or there significantly alter a kid's development. Most of the improvement comes from practice, skill development, and work in the weight room. It doesn't come from getting cycled in for 2 minutes around a TV timeout where the freshman barely even breaks a sweat before he's taken out.
As for why UNC has a deep bench -- that's also obvious. It has a deep bench b/c it has a lot of highly-rated kids who are still in college. If you look at UNC, they start 2 seniors, a jr. who was a McAA, and two former 5* recruits who are sophs. Then, off the bench, UNC brings in a Sr.. big James), a jr. big who was a 5* recruit (Hicks), a soph. former 5* prospect who was a McAA (Pinson), and a a Jr. guard who was pretty highly regarded as well (Britt). That's a lot of veterans with decent talent. The freshman you're mentioning are the 10th and 11th men at UNC. They are hardly critical pieces to UNC's squad. Duke's just not in the same situation b/c it had 3 freshmen declare for the NBA last season.