In all honesty, as much as I like Roeder - he is Shepherd's fall guy ultimately because he is a 'yes' man. The real reason as to why a Hitzfeld or O'Neill wouldn't come to Newcastle, is because they wouldn't stand for interference from the chairman. He has too much power and say at the club, and for that reason we are ultimately doomed to fail until he is removed or leaves.
A present, Shepherd is killing the club - it's in terminal decline, IMO.