I think KF's record vs Fitz is easy to explain (just like his record against McCarney, etc) - Iowa has "played up" to good teams under Ferentz and "played down" to inferior teams. I think it's a chip on the shoulder type thing. Ferentz has punked several Michigan teams that Iowa had no business beating talent-wise - the Fitz's and McCarney's of the world have returned that favor more than a few times.
I think the KF record against Fitz and McCarney and a couple of other coaches at lesser teams on the yearly rankings is even more easy to explain. Not only did McCarney and Fitz play with more of a chip on their shoulders but they took more chances. They knew they needed to take chances, run exotic plays because they didnt have the horses. NW and ISU both sell out on defense to stop Iowa and run crazy stunts and blitzes. Many times it works, Iowa plays conservative, and cant make a big play sometimes.
After KF's 2001-04 run a lot of coaches knew they couldnt go head to head with the hawks so you have to play "around" them to win.