For sake of comparison, here are Pelini's bad losses and ranked wins at NU. I am not trying to make this a Bo vs. Riley thing, just showing the info. I do give credit to Bo for limiting the bad losses. He just didn't win "big enough" to keep his job.
2008 - No bad losses and no ranked wins
2009 - No bad losses, ranked wins vs. #20 Oklahoma, #22 Arizona
2010 - Bad losses against Texas (borderline bad loss in bowl game against Washington), ranked wins vs. #17 Okie State #7 Missouri
2011 - Bad loss vs. Northwestern, ranked win vs. #9 Michigan State #12 Penn State
2012 - No bad losses, ranked win vs. #20 Michigan
2013 - No bad losses, ranked win vs. #23 Georgia (bowl game)
2014 - No bad losses or ranked wins