Advisory Circulars, although not regulatory, are nonetheless used by the FAA to go after folks for 'unsafe practices'. What about AMA'ers who know not of AC 91-57, but use the AMA Safety Code?
http://www.modelaircraft.org/files/105.pdf
(c) Not fly higher than approximately 400 feet above ground level within three (3) miles of an airport without notifying the airport operator.
Plus the FAA wants to use '5 miles' in their latest revision of a non-reg? Let the lawyers duke it out I guess...
One last thing, the FAA may be slow in implementing all this due to ICAO rules/proposals, implementation of ADS-B (google it), and the fact that some countries don't have a 'spotter' requirement for FPV.