The real problem, IMHO, is the ambiguity of the legislation, the unwillingness of the CAA (and its foreign equivalents) to commit itself on certain subjects, and (fortunately!) the lack of case law.
The last one is due to lack of appropriate accidents, presumably, because one is unlikely to get caught while in the air, and when one has hit the ground one is no longer VFR on top
Lots of IMC Rated pilots have flown airways (Class A) in the UK, France, Spain and elsewhere. If you know the rules (which you won't from bog-standard IMCR training done by an instructor who has only got the IMCR himself and probably got even that as a grandfather right 25 years ago) and sound good on the radio, and have a fairly serious plane, nobody is likely to question it. I've been abroad quite a number of times this year and not had even my passport looked at, ever, anywhere.
Most instructors don't have a clue either about these esoteric issues so how are PPLs supposed to know chapter and verse?