Looking at what Moos did at his prior job is the exact opposite of a "rare situation somewhere out there".
Leach at TT 47 conference wins in 10 years 2000-2009
MR at OSU 52 conference wins his first 10 years(apples to apples)2003-2012
I think we have different ideas of what "trending up" means. Leach's first three seasons at WSU:
3-9
6-7
3-9
MR 2-1 vs Leach
Both very good coaches who have proven they can beat more talented teams when their systems and the players to run them are in place.
Once again, the situations and expectations at each program were and are completely different.
Stating that Leach took a dip in year 3 of his tenure at Washington State as some sort of evidence that Moos might or should retain Riley at Nebraska simply because he happened to be the AD there at the time is a spectacular reach at best
Moos hired Mike Leach, for one, so had a vested interest in his success, and their program improved under him the first 2 years of his tenure. In spite of a dip in year 3 (which still had the team performing at least at or still above the level they had under the previous coach), he has improved since, and evidence existed he would do so, thus the continued faith Moos (correctly) had in Leach.
It is a rare situation in that a coach had a setback in year 3 of his tenure (relative to what he had accomplished in years 1 and 2), but still ended up improving the team greatly in succeeding years. Mike Leach did, but once again, he also had greater success in his first 2 years there than the program had for many years prior.
Comparing coaching records is fun, but Mike Riley won 43 conference games in his first 10 years at Oregon State to Mike Leach's 47. You're (conveniently?) excluding his first 2 years at the program, 1997-1998, where he won 2 conference games total. Mike Riley also had the benefit of playing one more conference game a year than Mike Leach did from years 6-10 in this specified 10 year window, so he played 5 more conference games than did Mike Leach.
And then there is Mike Riley's 53% win percentage at Oregon State compared to Mike Leach's 66% win percentage at Texas Tech.
Washington State has progressed substantially under Mike Leach, while Nebraska has regressed under Mike Riley.
There really isn't much more to discuss here.