I once liked Carter on Inside the NFL. Last year, he just started to sound moronic to me with his comments. Now, he isn't worth the time.
Keyshawn's "system" statement still sounds goofy to me. A trained back-up may know the offense and perform adequately in relief, but that does not mean Brady is a "system" guy and therefore is not a major contributor to the past success of the system or would not be a superstar elsewhere.
Some players respond well to structure, some do not (Vrabel wasn't a great fit in Pittsburgh, Harrison was viewed as done, Branch is not flying high in Seattle and we will see what happens to the money corner in Philly). New England has an excellent, structured system and selects players at the right price with the right attributes to fit the requirements of the system. But to say the overall system is responsible for the particular results would be the equivalent of saying a steam propulsion system would drive a locomotive the same way whether you use coal or uranium as the source of energy.
While I would love to see Cassel throw for 4500 yards and 40 touchdowns with a 100 QB rating if that system theory holds true, I suspect basic abilities and the experience factor make that result unrealistic. Cassel has been here long enough to avoid a learning curve figuring out the system, now it's time to see how far his abilities can carry him.