If they bought into Shanahan's theory they would be using his scheme of zone blocking. Amazing that they don't since two of the best running teams used it last year. If you don't use zone blocking then running backs aren't easily replaced, but they still don't really deserve huge contracts. Backs break down too easily and far too young to give them a huge commitment. Best backs are ones that beat other teams with big receptions, especially converting 3rd downs. Besides the best teams are the ones that run the ball well, but don't try to overdo it. You still win with passing in the NFL, as the Steelers proved this year. They never win the title if the old Cowher style was used.