Fuji,
To put it in very very very simple terms for you;
In ceratin classes of airspace your aircraft needs to be equipped with certain serviceable equipment.
In class G there is no requirment for the aircraft to have a serviceable VOR even when flying IFR in IMC.
That means that you can fly an aircraft with a VOR that has 60 to 80 degree errors perfectly happy in class G provided that you do not rely on the accuracy of the VOR to ensure separation from terrain, controlled airspace or other aircraft.
Do you now understand the difference between a requirement to have equipment fitted and the requirement for equipment to be serviceable before using it?
I think that those who advocate relying on ILS and VOR non-FM immune systems in class G are saying the aviation equivalent of "driving a car with defective brakes is OK if it has an MOT".
It is a commonsense safety issue!
Regards,
DFC
PS: Reputable schools do not rely on non-FM immune equipment.