It is a 'myth' and therefore can be used as such to represent that particular idealised image of Australia. I didn't mean it wasn't still used- it certainly is- but I think writers are also catering to their perceived audience as well. It can be used as a symbol- of the vastness, of the supposed 'freedom' and space. The 'bush' on the other hand is perhaps less esoteric- it can refer to any area outside the larger cities- even a regional city- as well as a more isolated area.