While they may be bad reasons for the pricing discrepancy you have to take in to context that every single thing in Australia is ridiculously expensive when compared to UK prices. Everything from electronic goods to clothing to food.
Demonising GW alone for price gouging in the Australian market isn't entirely fair. Where they appear to have suffered is in the loss of sales over the last couple of years and the damage that seems to have caused to the player base. From memory GW had a 10% drop in sales the previous year and then restricted direct sales from the UK, but no annual price increase in response. For this to then translate to only a
marginal increase in local sales would seem to me to indicate stagnation in sales and/or player numbers.
However unless you have access to the actual data it is impossible to tell.