The privileges a pilot may exercise by virtue of his licence are mitigated by various factors. One, for example, is the class and location of the airspace he is flying in. Another, is the type of aircraft he is operating. For example, if he is operating a PFA type, he may not operate in IMC or at night, not because of some reduction of his licence privileges, but because of the restrictions associated with a PFA type.
The FARs list the rules associated with operating an N-registered aircraft. That you can fly an N-reg type at all is because the FARs expressly permit flight in an N-reg aircraft by the holder of a licence issued by the territory in which he is flying. This right is granted, not by the ANO specifically, but by the country in which the aircraft is registered.
2D
A LINE OF COUNTERARGUMENT
There is a line of argument that goes along the lines "What have the FARs and the FAA got to do with anything?" If I hold a valid CAA/JAR licence, and the aircraft is a class/type that I my licence is valid for, and we are sitting here in England, what have the Americans got to do with it?"
In my opinion, the answer to that is:
An N registered aircraft may only fly at all because the state of registry has given it a certificate of registration and airworthiness. These only remain valid if the aircraft is maintained to the schedule set down in the FARs and operated by those whom the FARs approve in a manner set down by the FARs.
You can no more pick and choose which of the licencing FARs you go along with, than you can elect to maintain it in accordance with UK maintenance schedules. The FARs govern the operation of an N-reg aircraft, because to fly contrary to the FARs is to void the registry and/or airworthiness of the aircraft. The CAA will not approve any activity that causes a foreign aircraft to operate in an unapproved condition inside UK airspace.
The same principle would apply to a G-reg aircraft. You could not take one to the US an holiday and start to forget about 50 hour checks, since you were no longer in the UK.