If designed correctly the systems could use new technology as it comes along. That means they should buy the design but not the componets, yet. Heck, they probably already own the design so no need to buy anything at the moment.
The issue, apparently, is that some of the components are about to cease being manufactured.
By ordering now, the Australian government can have them manufactured as part of the last US production run.
If the Australian government delays, it will have to eventually pay for the whole production line being started up again.