And again, it's been said on here numerous times, but Spurrier's failure wasn't a condemnation of his system's inability to succeed in the NFL. It was a condemnation that you can't be on the golf course for 10 hours a week and then succeed in the NFL with a shitty roster.
True. But NTP failed with the Dolphins. Butch Davis didn't work out very well in Cleveland. There are plenty of examples, and with enough of them teams will think it's more a matter of recruiting and overwhelming the opposition with superior talent.
Harbaugh in SF is a decent counter-example. Coughlin is another, but he made the jump 20 years ago. but most of the successful NFL coaches were NFL coordinators or NFL retreads.
Super Bowl winners the last 10 years:
Coughlin - Jaguars head coach
McCarthy - Saints coordinator
Payton - Cowboys coordinator
Tomlin - Vikings coordinator
Dungy - Bucs head coach
Cowher - Chiefs coordinator
Bellycheat - Browns head coach
Gruden - Raiders head coach