I believe the regulations you cited only apply to aircraft/vehicles on active airport surface movement areas (e.g. taxiways and runways).
See: http://www.faa.gov/other_visit/aviation ... o15006.pdf
Unless this has been superseded.
Hmm... My AIM quote was out-of-date. Here is the 2017:
4-5-7 c. 3. ADS−B is intended for in−flight and airport surface use. ADS−B systems should be turned “on” −− and remain “on” −− whenever operating in the air and moving on the airport surface. Civil and military Mode A/C transponders and ADS−B systems should be adjusted to the “on” or normal operating position as soon as practical, unless the change to “standby” has been accomplished previously at the request of ATC.
Which mentions the entire "airport surface", not just the movement area.
And according to that SAFO you linked to, it says to leave ADS-B enabled after landing, and all the way up until parked at the gate. And also to enable it before pushback (which would typically be in non-movement areas). So that document seems to contradict itself.
But there's still the matter of being at the gate with ADS-B. That's the real debate at hand. I'm having trouble finding documentation (other than your source) that specifically talks about ADS-B at the gate.
On top of that, does anyone know if there is actually a way to disable ADS-B on an airliner (i.e. a Boeing or Airbus)? It is my impression that when a pilot puts their transponder into STBY mode, ADS-B is still transmitting as usual. Perhaps I am wrong.