"a certain aerodrome" I think you will find it is all aerodromes where the aircraft apron is part of the security controlled area. Some aprons were large enough to allow a delineated area for non-screening of pilots or pax boarding GA aircraft. Just like at Perth airport where you can board your plane anywhere on the GA apron then merrily taxi amongst the big boys.
Yeah. I only fly to a few airfields and it is Learmonth that stands out as having this anomally. DBY, BRM, PD, KA, GEL, and PH are all tickety-boo. I don't doubt that there are others and your reason makes sense, as the LM apron is not very big.