I recall the example from SP: Stick of Truth where the alien probing sequence was removed and replaced with a crying koala. I can list more titles that are not available from that region: Hotline Miami, Manhunt, Sludge Life & etc. but there are games that faced censorship: Saints Row IV, Fallout 3, Postal 2, Outlast 2. I notice that it tends to happen with games depicting content involving violence, drugs or even sex (but let that fly in movies and TV).
Simple solution: DO NOT use an AU account on Steam, instead consider a region change or an alt account set overseas where you can access “banned” games that aren’t not sold in Australia (as their ratings board has no jurisdiction over foreign copies). Even if you have a foreign physical release: those are classified in their country of origin, isn’t that enough? A Japanese (CERO) D 17+ rating is similar to a MA15+ - R18+ classification.
Australia was historically a smaller market that is physically far away from America and ( and had fewer trade links with Japan). Australian TVs were PAL while America and Japan used NTSC, which added a whole other layer of complexity. This meant that PAL production lines were geared towards the European market, with Australia getting the excess. Those copies then had to be shipped across the Pacific Ocean, which is expensive. Combine a smaller, lower-priority market with longer, more complex shipping, and manufacturers charged more to make a profit. This set a standard price for Australia which persists even today.