In Aus, the NFC terminals (Paypass/Tap&Go/etc) all use the same protocol, in the same way that all the Visa/Mastercard/Bankcard magstripes were written in a common industry format. American Express/Diners were outliers and originally required their own terminals, which is why they always had to fight an uphill battle to be accepted by smaller merchants. These days, the EFTPOS machines and banks have facilities for multiple card types, and the EMV standards encompass implementations for both NFC and Chip&PIN.
The NFC in smart phones use the same RF protocols that are in place for other wireless payment cards (and can easily be updated to provide slight protocol changes if necessary). The hard part is that Apple needs to partner with the big payment providers to allow their generated 'one-time' payments to be correctly cleared in the same way any given issued credit card is cleard. Currently Visa/Mastercard/etc do this for their branded cards and are the biggest players in this sector, which is why Apple needs to work with them to avoid having to set up any of its own infrastructure (beyond it's internal payment gateway and integration with backends at Mastercard/Visa/etc).
There is no reason once deals are struck between Apple and Visa/Mastercard in Australia, that any merchant here would require a change to their installed Paypass/Tap&Go systems. There may be some technical integration problems between Apple and Visa/Mastercard that need to be sorted out first, but that work has most likely already been done (or mostly done), otherwise Apple wouldn't have announced it with such fanfare.
Like everything, for some reason these deals take longer to happen in Aus when the technical and business solutions may have already played out elsewhere in the world. Take iTunes for instance; we had to wait much longer than the US, because it took longer to get the distribution agreements worked out thanks to our local incumbents with pre-existing contracts being reluctant to renegotiate and move with the times.