My local family history society gives A*****y their cemetery indexes etc. in exchange for free access to the site, and I think it may work the same with the government documents. As far as I know the library edition of the site is available free of charge at all/most libraries in Australia, and I doubt if anyone is paying for it. I suppose they see it as a win/win situation where the government doesn't have to be involved in the scanning, indexing, hosting, and the site gets free carrots to dangle. I think one might be winning more than the other though!

As for SA records, possibly the site is simply looking at where most of the demand is coming from. They will milk dry the early records for the eastern states as these are likely to be the ones that bring the punters in. Then again, SA might have just told them to b*** off!
Debra