iowa has had a virtually identical staff since KF was hired. The same could be said for Fry's first 10 years. Same can be said for Missouri and Pinkels staff.
Sure, teams can win with constant coaching turnover- but its really reserved for top programs and top teams. Look at the gators this year, they lost their O-cordinator and suddenly their offense is less than impressive.
To some extent I am sure it is just pure loyalty to the program (Norm Parker) but some of it is also the fact some of the assistants don't set the world on fire (Ken O'Keefe).
You take the good with the bad in this case. If you get great coaches and they do great things pretty much every school will lose them eventually. If you get good coaches who do good things they might stick around.
The good vs bad with O'Keefe is his offense is consistent but he is not flashy. Because of this he does not attract top level jobs and sometimes his offense sputters and underachieves.
Frankly, the fact Norm Parker is still at Iowa is surprising but a great illustration that sometimes coaches can be very loyal people.