I never get the "ESPN hates <your favorite team goes here>" conspiracies (NU fans aren't alone in feeling this way about their school, btw). Certainly they have some individuals that aren't big fans of one program or another, but for the most part, I think the network's coverage is fair and unbiased. At times, I think honesty is confused for hostility.
From what I saw, they gave Callahan and Pederson's dismissals plenty of coverage, and they covered Osborne's hiring as interim AD, as well as him appointing himself interim HC. The coaching search got daily coverage on multiple shows. There is one simple reason that Pelini's announcement didn't get as much air time, and that is because of when it occurred in the news cycle - right in the middle of the NFL game day and BCS announcement day. If it had been announced on Monday, it would have gotten more coverage or at least higher billing, although it would have been behind coverage of the Patriots / Ravens game and the Sean Taylor funeral.
