Perhaps operations in AUS differ from the US. However, I routinley fly on an IFR flight plan (without cancelling it) outside of a radar environment, cleared for a visual to a non towered airport as well as oceanic and remote operations. I guess Qantas have to cancel IFR every time they pass into the Oaklands airspace coming out of here, since radar service is terminated and they are told to sqawk 2000, fascinating stuff.
My experience of flying over 2000 flights into uncontrolled fields under IFR and cancelling on the ground with the airspace remaining cleared for me and operating under an IFR clearance tell me otherwise.