The full ICAO procedure is that when a pilot thinks he may land with less than Final reserve he declares “Minimum Fuel” . When he knows he will land with less than final reserve he declares “Mayday Fuel” . This has been used by the rest of the world for sometime, as others have mentioned . It is a good thing Oz has finally caught up (well they didn't take the first bit it seems) . With its remote airfields and lack of facilities fuel can become a scarce resource and having a predictable procedure that is internationally recognised helps to mitigate.
The PAN call is not understood in a lot of countries, hence the use of the word Mayday . Remember ICAO wanted the one procedure throughout the world .
If you plan your flight correctly you shouldn't need to use it .
LB excepted of course .