Never mind betting -- the NFL is an entertainment business. Some possible game outcomes are more entertaining than others and will produce more fan interest and advertising dollars than other possible game outcomes.
The sport isn't flat-out fixed like wrestling or boxing or the NBA. The are just some nudges here and there in the direction of the favored outcomes. Sometimes it's enough to change the outcome, and sometimes it's not. It's definitely possible to play well enough to overcome the refs; teams do it all the time