When Fantasy Football really started becoming popular maybe 6-7 years ago you could never have enough running backs. The likes of Marshall Faulk, Edgerrin James, and Larry Johnson were always number one on every team's wish list.
Now with the shortage of frontline running backs, team owners that made the switch last year to loading up on wide receivers are reaping benefits. Teams banking on RBs like Willie Parker, Ryan Grant, and Tim Hightower are probably struggling while starting 3 WRs is becoming the "in" thing to do.
NFL teams have increasingly switched to a pass oriented offense, especially in the red zone. Fantasy owners are realizing starting a Miles Austin, Johnny Knox, or Austin Collie are better options that a 2nd running back. An example is the Pittsburgh Steelers who won last years Super Bowl ranked 23rd in the league in rushing last year. Scour that waiver wire, there is a much better chance you can find a diamond in rough WR that can help you to fill a bye week opening or an injury than starting a short yardage running back and hope he gets a cheap touchdown.