Spy logic does not grant veterancy for aircraft or naval vehicles

Out of sheer curiosity. I've read the ARES documentation, specifically the section about veterancy effects and spy and read this note:
This only works for VehicleType and InfantryType factories at present. Also note that infiltrating any VehicleType factory (i.e. War Factory or Naval Yard) will only make land vehicles start veteran - Naval vehicles cannot be made to start veteran through spy infiltration logic."
Is there a limitation in the game that prevents granting veterancy to aircraft and naval vehicles? If so, what is it?