Dear Pierre
If you worded your questions in a positive manner, it would be much more helpful and would lead to a better response.
As it is, I just feel that you made a vague and generalized statement that sounds like point scoring and your assertion that you support GA comes across very much as "he who denieth too strongly."
Airfield strictly PPR. Un-notified light aircraft calls declaring they're inbound... but unable to make a Instrument Approach.
Okay, let's try to explain this ...... Airfield strictly PPR.
So un-notified traffic now becomes notified by r/t. (you did not say PPR by telephone.)
Pilot communicates clearly by establishing the limits of his licence privileges - weather was okay when he planned flight and departed, but now he has listened in on frequency or to ATIS and realises he might have a problem. (You did not give a weather trend/history for this field and the area, or where the inbound pilot had come from )
He talks with ATCO, confirms situation and then implements excellent contingency plan, diverting as planned. (You said that the diversion was well planned)
See the problem? You give so little information that the data can be manipulated very easily.
Maybe it would be a good idea to think through what you are trying to achieve before you post next time, since there is probably a good topic to discuss here, if raised properly.