^ I don't get it.
Inflation = price increases (in this context anyway)
As the GST is a percentage, it doesn't matter if inflation is 1% or 1000000% - the govt still gets its 10%.
The problem for the Govt is the lag effect of inflation and their ability to collect GST. I'd say at the moment it is a minor problem, but it'd be a major problem during hyperinflation (although that's just one of many problems then).
Edit: The rest of your post is spot on, like:
flashinthepan said:
Wage increases on the other hand are not keeping pace with inflation as our standard of living is being erroded yielding positive decreasing returns to the ATO in that reguard.
Edit2: I just realised that is incorrect too.
The ATO wins in an inflationary environment, as tax bracket changes can lag due to deliberate Govt policy sluggishness. Eg, in 5 years, maybe we'll all be on the top tax rate, merely due to wage (and CPI) inflation, without them changing the tax brackets.
Where the ATO really loses is 'deflation'. I don't see that happening anytime soon.