The NFL is a pass-first league. Heck, you could argue that it's now a pass-second and pass-third league at this point. Successful teams -- the Patriots, Packers, Giants, Saints, even the Pittsburgh Steelers -- rely on big-time QB/WR/TE connections in order to move the ball and score points. Running games exist as a change of pace to a downfield passing attack. Most successful offenses have 2-3 back committees and tend to shy away from the prototypical "feature" back.
Teams that have the great QB and playmakers at WR/TE can succeed with minimal support from the running game. Tom Brady makes the Super Bowl with Danny Woodhead and Benjarvis Green-Ellis carrying the ball. Eli Manning's Giants win the Super Bowl but didn't have a single back put up 700 yards (leading rusher, Bradshaw, a 7th round pick). Aaron Rodgers nearly went undefeated with an undrafted free-agent (Grant) and a 6th rounder (Starks) splitting carries.
The inverse, however, is not true. Ray Rice has not been able to carry Joe Flacco and the Ravens middling WR corps to a Super Bowl. Maurice Jones-Drew cannot overcome the awful that has been Jacksonville's QB play during his career. Adrian Peterson's only sniff of glory came in a season where Brett Favre pulled a Lazarus act and put up great aerial numbers. Last season's fluke aside, Frank Gore hasn't led the Alex Smith-burdened 49ers to anything resembling good for the majority of his career.
The feature back is a dying concept. Successful teams have figured this out while other teams are stuck in neutral, trying to scheme and gameplan to get touches for their running back.
Drafting Trent Richardson is dinosaur thinking -- especially when you have the ability to get players who can help you pass the football or defend the pass instead. If you're drawing up a blueprint for building a great team, you'll need lots of good WRs, TEs, DBs, DEs, and a great QB. You won't ever need a great RB.