Guys, didn't you know that Jim Brown was made of glass because he wasn't man enough to play until he couldn't walk?! Sorry, I found danny boy's pipe...
Danny, a brief education for you here. Franchise running backs are VERY rare, and within this scheme and in this era are largely ineffective. Knock it off with the LT argument...ever hear of a guy named Michael Turner? But, he's a backup so you likely think he sucks out loud. Like every position in the NFL (SITUATIONAL FOOTBALL!!) no one running back does everything perfectly. Certain players have certain skill sets and they should be utilized accordingly. That's what we call coaching. A guy like Marshal Faulk could never do what Larry Johnson does, and vice versa. They have very unique and very gifted skill sets. Sammy Morris and Laurence Maroney are two different kinds of (very good) runners. Morris is a linear runner who is great working behind a fullback or pulling guard and hitting a hole hard. A guy like Maroney is a one-cut type runner who is much better suited to work out of an ace-type set and follow a zone blocking scheme. His awareness will improve with time and coaching, his tallent is undeniable. Once he develops better continuity with his linemen he's going to be a star. But he's not a 30 carry guy. In fact, having a guy who carries the ball 30 times a game is symbolic of a lack of depth in a roster. Heck, the Rams drafted Leonard to compliment Jackson. There's a reason why backs on average have the shortest NFL careers. They take tremendous abuse and tend to wear down much faster than other positions.
It is far better for THE TEAM to have a stable of capable and diverse backs who can execute the correct play for the situation. IE; Would you want Kevin Faulk pounding the rock for an inch and Heath Evans running wheel routes out of the slot? This game is not about having "that dude". The game is about having 53 capable players who all bring different things to the table. Now go brag to your classmates about how much you learned tonight. You owe me 10 bucks.