Every coaching staff is different. Different guys have different experience in different areas. Bo is a defensive mind. He's the head guy, but his specialty is defense. Watson is an offensive guy. But we knew from day one that Bo was going to bring changes to the entire team. The fact that Bo isn't drawing up offensive plays or overseeing the strategy on game day shouldn't bother anyone. Bo is a professional and so is Watson. They can be trusted to manage their assignments. Bo's job as a head coach is larger than knowing every play in the offenses playbook. As long as he and Watson have a good working relationship which allows them both to do their jobs better, the world is as it should be.
Now if the situation is as the first poster described Callahan and Cosgrove's working relationship, it's a recipe for disaster. But judging by the results of last season (a top 20 offense and a defense that jumped over 50 spots from the previous year), nothing is wrong with how Pelini chooses to conduct his role in the offensive strategy. His leadership qualities alone positively affect both sides of the ball.