It's amazing to me to see how quickly the FAA will file and win an enforcement case on a pilot taking an aircraft and a release with a wrong N-Number, or a pilot who parks an aircraft following a marshaller who has the wrong colored wands (per FOM discription, etc.) - yet - the same inspector will have no idea on how to handle a company who pushes pilots way past fatigue and threatens to suspend them for calling in sick.
Now, to be fair, there are reasons why the N-Number is critical on a release. For one, the dispatcher partially shares the responsibility for 121 ops with the Captain. The dispatcher is not in the loop when the N-number is wrong on the release! The MEL staus, BOW, weight and balance (if it's centralized) - it's all wrong on the paperwork and it causes a moment of concern as to how many other parameters were wrong on that flight.
But really, the big fight in safety is operational deviations that cause perfrectly good airplanes to be flown into the trees or ground. That's where the FAA is least capable of helping out, historically. They really like to make sure the paperwork looks nice.