Tressel went to Ohio State. It is not as if he went to Vanderbilt and turned it around. Having a hotbed like Ohio to recruit is definitely big. Plus, there was talent already there at Ohio State before he got there. Cooper just could not win the big games.
Harbaugh is the real deal. A family tradition sure helps though.
Paul Johnson had to go to Navy before getting Georgia Tech. Besides George Welsh, not many coaches survive the academies (Navy and Army that is)
There are plenty of examples of IAA blowups like Terry Allen at Kansas, Wulff at Washington State and many more. Yeah, there are a few that have made it but location helps because you need the recruiting base.