Interdiction from frozen areas?

[batou]

I do not understand why frozen enemy land regions generate interdiction points against fleets. Is this WAD? These areas are frozen and not at war, how are they representing (to quote the manual):

"the disadvantages inherent whenever moving Fleets through waters that can be controlled by enemy land based airpower and small naval vessels (like PT boats). Even if an Air unit is not physically present, small numbers of aircraft and small ships (units not seen on the map) can cause sufficient damage to forces that sail by to make these land bases hard to ignore."

If forces in the Vichy controlled Morocco, Tunisa and Corsica were causing sufficient damage to Allied shipping when moving from the Atlantic to the Central Med then I asume the Allies would be at war with Vichy at that point. Is there something else this is modeling?