To summarize, a Nebraska coach will never be retained for simply beating Iowa and will certainly be fired for losing to Iowa too many times, while an Iowa coach will never be fired for losing to Nebraska and will be certainly get a lifetime contract for beating Nebraska.
Riley didn't just get fired for losing too Iowa. He didn't beat Wisconsin either...
19-19 worse 3 year record in 50 years and 4-8 worse record since 1961. Higher administration and fan base recognized this was a bad hire by a AD that failed miserably as AD at Nebraska.