I don't see any problem with them paying someone in Canberra less than they pay an equivalent person in SF, but I think it's disingenuous to make it about "cost of living." Someone with kids and a mortgage has a much higher cost of living than someone without (in the same location) but do they automatically get paid more?
The local (tech) job market determines what the workers will accept, not (as others have noted) the cost of rent or beer.