It does seem odd there is such a large price difference between the steam version and the non-steam version. But there is no chance of SE doing anything to address it.

Aus players have previously complained about being lumped in with EU countries and being forced to pay in euro instead of GBP or god forbid our own currency. Even though we have zero to do with the EU as a country we were just lumped in with France and the rest, and SE have never changed how we're billed.

I suspect someone at SE in the early days didn't do their research properly on these sort of currency/nation/union differences and it probably does warrant a review by someone who has looked at a world map.