But for long overwater flights (or long flights over hostile territory) AAR is pretty much a necessity.
There's your answer. The RAF's helicopters were designed/procured to move stuff around the UK and northern Europe, not to make long flights over water or hostile territory. Granted it didn't quite work out like that...
If the USAF/USMC's entire intended theatre of operations fitted between Boston and Cincinnati would they need/have AAR capability ?