As your link itself explains, the vast majority of those vacant properties are either a) holiday homes that are empty outside vacation season, or b) "areas with declining population where dwellings are simply abandoned by owners who can’t sell their property". Vacancy rates in major cities are remarkably low.
it may not be a big problem at present, as there is a huge real estate boom in Australia. But when there is an economic downturn these regulations are going to hit older areas extremely hard, just like they have in many other nations.
Property values in Australia declined by 4.5% last year. Forecasts are for around 5% growth this year in my city (Brisbane), but continued declining prices in Canberra, Melbourne, Hobart and Adelaide.
Huge real estate boom fizzled at the end of '09 / early 2010.
