ICAO ARTICLE 5
Marauder,
ICAO Article 5 clearly describes the right of a private, non scheduled, non revenue flight to overfly the airspace of an ICAO contracting by an aircraft of an ICAO contracting state.
A flight plan needs to be lodged, or notification given to the airspace owner.
I say again that most 3rd world countries do not understand ICAO Article 5, even if you sit down with them and go through it word for word with them as I have.
Given that status, as previously posted, even though it is NOT REQUIRED, lodging a request for overflight clearance is the only thing they understand and it fits in with their comfort zone and lack of knowledge.