They hit harder than most defenses. Trying to win a ball control game against that bunch is going to require good running backs who can rotate in and share the load.
Trying to give that many carries to one back is going to get him battered and bruised all too quickly.
Think of how tired and slow Ryan Grant looked in the last few games of 2002, and how sloppy he had played in those last 4 games compared to the first 8 games. I'd even argue that he started looking very slow and sloppy around the time of the BC game. Even though he had a pretty good day, he was getting knocked down with one hit, as opposed to breaking tackles.
Navy: 10 carries for 13 yards
Rutgers: 18 carries for 68 yards
USC: 10 carries for 16 yards
NC State: 21 carries for 68 yards
Thankfully, we have three very capable ones (Love, Price, Williams), and another high talent freshman who is a pretty speedy bruiser (Young).