I have no clue why the Aussie use the plastic. There was some Aussie 7.62x51 ball that was imported a while back and some of that also used the plastic blister pack.
just remember, if you buy this stuff, it is a steel core bullet, SS109 style. It doesn't have a green tip because Australia never issued M193.
The Aussie 7.62x51 was considered very good ammo. If this 5.56 is as good, then this would be top notch stuff.