From what i understand, USPS use commercial passenger flights to transport - and there are little to no flights comming into Australia. Where as DHL & FedEX have their own dedicated cargo flights i believe?
Just FYI, anybody waiting on a USPS delivery - my 'express' shipping from BBTS sent on the 28th July didnt arrive until Thurs the 9th September... so 6 weeks USA to Perth.
According to tracking it moved along fairly normally until it arrived at an intermediate airport in Hong Kong on the 14th August & stated 'delayed awaiting flight'. It stayed that way until the 7th September when it touched down in Au (and the tracking changed to 'departed' on the 14th August, which im quite certain it didnt - pretty sure it sat in HK for 3 weeks waiting for a flight).