The new carriers the Royal Australia Navy (RAN) is looking at getting will not have catapults as far as I know. I can see no other practical application of carrier-based training other than to be operationally deployed from carriers. I would have to agree with you that RAAF Hornets - Super Hornets at least - could well be seeing action on USN carriers.
The RAAF won't be having operational F/A-18Fs until 2010 though. Perhaps being trained for carrier operations on the Super Hornet is an interim training package for future capability allowing RAAF F-35s to operate off RAN carriers? Getting some training early on will help the RAAF develop instructors with a good foundation in this skill set.