Today was the day that Steam finally added support for the Australian dollar, and also the day that a number of games stopped being sold to folks down under. Steam requires publishers to explicitly set prices in regional currency for a game's to be sold there, see, and some folks just haven't done that yet. Which is a problem if you currently want to buy such games as Vermintide 2, Factorio, Ori And The Blind Forest, Return Of The Obra Dinn, The Binding of Isaac: Rebirth... some good stuff. I imagine oversights will soon corrected but it's an awkward teething problem. A bit of a sticky wicket.
So! Australians now pay localised prices in Australian dollars for Steam games, rather than paying in US dollars and having prices converted. That seems to means yes, game prices there have gone up a wee bit too.
It's not a surprise that some games have become unavailable with the switch. Valve warned developers in advance that this would happen, making clear that they'd need to set AUD prices for their games to continue to be sold there and even recommending price points. Some still have not set Australian prices (hey, life's a lot) and so away go their games until they do. Kotaku Australia have ferreted out many of the neat-o games temporarily (hopefully?) not sold on the Australian Steam store.
Australians who previously bought any of the games that are currently unavailable do still have them in their Steam library, and can still download and play them. It's only would-be-newcomers who are affected by this.
Developers, these nice Australians would like to give you money; please help them do that.