I also happen to think if Cowher had stuck around longer, the Steelers would have either lost Roethlisberger after he requested/forced a trade out of town, or he would have been largely relegated to being a game manager in deference to a power running game for a sizable chunk of his career. In other words, a Dan Reeves/John Elway type of relationship.
http://static.espn.go.com/nfl/playof.../01056576.html
Undervaluing the QB position and treating it as an afterthought is OK when you have schlubs like Tomczak and Stewart under center, but not when you have a bona fide franchise QB on the roster. Hell, Roethlisberger was already starting to show signs of chafing under Cowher/Whisenhunt even before Cowher left. At the time, a lot of people chalked it up as immaturity on Roethlisberger's part, and while I also thought that was part of it, I still believed there was more to it than that. Still do.
Example: setting Roethlisberger loose against the Bengals, Colts and Broncos in the 2005 postseason and then doing a complete 180 and going ultra-conservative against Seattle in the SB.
Managing QBs = Cowher's Achilles' heel.