It is, actually (though it should be noted, for some reason it includes NZ as part of AUS, so the Corkscrew at Rainbow's End shouldn't count). Here's all of RCDB's listings:
And, for good measure, here's all the defunct ones:
Using this, Australia technically has the most coasters with inversions currently than it's ever had, with the closest time period being between Lethal Weapon's opening and Thunderbolt's closure (excluding the gap between when Big Dipper II became Cyclone), when there were 5. But, taking into account the places these coasters are, that time period had:
1 at Movie World, QLD
1 at Wonderland Sydney, NSW
1/2 at Dreamworld, QLD
0/1 at Luna Park, NSW
Compared to now, with:
2 at Dreamworld, QLD
1 at Movie World, QLD
1 at Adventure World, WA
1 at Luna Park, NSW
1 at Gumbuya World, VIC
They're much more spread out, and (including the recent closure of Arkham, and relocation of Buzzsaw) that may be why it feels like there are less.
*1 at Sea World, QLD