Great point on NBC. Remember however that NBC is owned by Comcast, whom has many other cash gushing revenue streams to balance out any possible softness across their, Comcast, other Lines Of Business's including NBC.
Another point of consideration here is that there are now to many media vehicles to watch games on. Meaning that maybe fans are saying "enough football is enough". Thursday -> then Sunday 9:30 when playing in London, 1:00, 4:00 8:30 -> then Monday night. Across ESPN, NBC, CBS, FOX, Yahoo, Amazon, Directv and on and on.