exemption to negotiate its TV deals because the entities that matter here are the individual teams, not the league as a whole. It'd be interested to see if the salary cap is ever challenged in court, though it might end up like the MLB's case. I suspect it hasn't because (a) the NFL does pay its employees, the players and (b) the NFL doesn't prohibit players from commercializing their own name, image, and likeness.
In fact, I'd be OK with the NCAA having a similar model: schools can keep their agreement on what they offer athletes and keep that side "amateur", while not putting arbitrary restrictions on the players profiting off their name, image, and likeness.
Funny thing? That's exactly what the California law does.