There is much more behind the success of Asian vehicles in Australia than just fuel economy. For years, local cars have suffered from an image of lower build quality, less refinement, poorer equipment levels and higher fuel consumption. The Japs and Koreans learnt a long time ago that the majority of buyers want more than just cubes and grunt. The old idea that you needed a big car for a family died out with compact SUV's. Medium sized vehicles offer similar interior space to Commodores (note - similar, not identical), without the burden of being physically larger and heavier. They are easier to park, stuffed full of gear that buyers want (which is either optional or not available on local cars) - the list goes on.
The Commodore/Falcon sized cars are losing popularity for many reasons, not just because they use more fuel. The Cruze will overtake Commodore sales within 12 months. Make the most of your VE's and VF's when they arrive - chances are the next "Commodore" will be a bit smaller and less "ballsy".