I think that Iowa loses more RBs than any other college team for all kinds of reasons. Seems like very few RBs play more than one year at Iowa. Here is a list since 2001:

A Comprehensive History of the Angry Iowa Running Back Hating God (AIRBHG):

2001:
-Ladell Betts, who had managed to put up respectable numbers for four years despite playing for some of the worst teams in the history of the school, gets hurt before what would have been his only bowl game

2002:
-Aaron Greving, the projected starter, gets hurt and misses the start of the season, quits halfway through

-Incoming Freshman Justice Hairston fails to qualify, goes to prep school, eventually goes to Rutgers instead

2003:
-Jermelle Lewis, a highly touted recruit who looked great as part of a 1-2 punch with Freddy Russell in 2002, tears his ACL
-Albert Young breaks his leg

2004:
-AJ Johnson flunks out prior to the season
-Freddy Russell goes pro despite being able to petition for an additional year, presumably because he couldn't wait to get his CFL career started
-Jermelle Lewis tears his other ACL
-Albert Young tears his ACL
-Marcus Schnoor tears his ACL
-FB/HB Champ Davis tears his ACL
-Marques Simmons misses most of the year with a high ankle sprain
-Sam Brownlee and his sub-2 ypc remains healthy and starts most of the year
-Damien Sims briefly moves to CB, tricking AIRBHG and insuring his status as the only Iowa running back of the last decade to make it through all four years completely healthy.
-Somehow Iowa finishes the season as Big Ten Champs and ranked 8

2005:
-Justifiably proud of his stellar work the year prior, AIRBHG rewards himself with a year off.

2006:
-In-coming 4* recruit Kalvin Baliey flunks out
-Corey Robertson flunks out
-Albert Young suffers a variety of minor injuries that, when combined with all the other leg injuries he'd had, leave him a shadow of what he was in 2005, when he led the Big Ten in rushing during conference play.

2007:
-Shonn Greene flunks out
-Dana Brown hits a girl and gets kicked off the team
-Jason Ford decommits from Iowa in favor of Illinois.

2008:
-Javon Pugh transfers after a mysterious suspension
-Promising in-coming freshman Jeff Brinson gets hurt and misses the whole year
-In-coming JuCo recruit Nate Guilloy leaves the team and transfers after spring camp
-Special teams gunner and garbage time running back Jayme "The Irish Car Bomb" Murphy suffers what I believe was the first of an estimated 7000 concussions. He would eventually be removed from the team for his own good.
-The Legendary Paki O'Mera begins his reign of terror on the Iowa depth charts
-Shonn Greene returns from a year of junior college and furniture movin to have the best season in school history and no one really notices this other stuff because EEEE

2009:
-Jeff Brinson gets hurt again
-Projected Starter Jewel Hampton tears his ACL before the season
-Adam Robinson and Brandon Wegher, both freshman pressed into duty, are hobbled most of the year.

2010:
-Brinson tries to escape by transferring to UCF, but AIRBHG hunts him down and tears his ACL again
-Jewel Hampton tears the other ACL, eventually transfers
-Wegher gets a girl pregnant and leaves the team never to return
-Coker breaks his collerbone in fall camp and misses the start of the season
-Robinson suffers a concussion, has grade issues, and eventually gets busted for pot at the worst possible time and is thrown off the team
-Even Paki O'Mera gets hurt

2011:
-Rodney Coe fails to qualify and heads to Community College
-Melvin Gordon decommits from Iowa in favor of Wisconsin-
-McCall gets hurt on his tenth career carry, eventually gets suspended for mysterious reasons, transfers at the end of the year
-Coker is suspended for a code of conduct violation prior to the bowl, eventually asks for a release.