Both Lost Symphony and Untold Tales both cost more in Australian steam store compared to US.
But the previous Vaulters DLC is the same price for both regions.

AU steam store is in USD and I was happy to buy the Vaulters DLC since it was the same price compared to US region. Doesn't seem right that the price for these 2 new DLC's are increased for AU region.

I am a fan of the Endless Series but seeing this disparity in pricing feels too unfair.

I am making a guess here but I believe that it has something to do with steam being bad with converting different currencies.

Both US and AU steam store pricing is in USD. There is no conversion of different currency.

Since I live in AU, I have to pay my bank foreign exchange fees when I buy things on steamstore in USD currency. (Again, there is NO AUD currency for the steam store here).

This pricing is decided by either the developer or publisher.

Interesting there is no AUD store, there is an NZD store!

I know that this is definetly not the only game thats more expansive in australia then in well the rest of the world, but people always said that it was a Steam-thing.

I would contact steam for the discrepency, steam is the one who sets in poker terms the 'vig' or the 'drop' on the games, and you may be seeing the fee % of the steam fee as the variance between.  

Steam has a bunch of pricing presets where you can choose a US price and they'll fill in other regions automatically.  The automatic regional prices are not direct currency conversions, but attmept to take into account pricing norms of other video games in those regions.

However, the developer/publisher can override any individual regions manually if they want.  (I would guess that most publishers don't override prices for most regions, though, because setting a good prices would require a fair amount of region-specific expertise. There are a lot of regions.)

For the preset of US $2.99, Steam's current auto-filled price for Austrailian Dollar is A$ 3.60, and for New Zealand Dollar is NZ$ 3.69.

Steam changes its recommendations from time to time, but the changes aren't retroactive for existing games unless the developer/publisher chooses to go back and apply them.  There is some disincentive to do this, because raising your price in any currency makes you temporarily ineligible for sales.

Steam is also gigantic and they may have special cases for some games that I wouldn't know about.  I have no inside information regarding Amplitude or Sega.

bump

I'm just telling you what shows up in Steam's developer UI when choosing a price to sell your game at.

It could be that they labeled it a currency because they added it at a time when they didn't have infrastructure for doing regional pricing in a single currency, or maybe they keep it listed as a currency to make it easier if they ever decide to start accepting a different currency in Australia.  I don't know.

But there's an entry in their list for Australian Dollars.