I know nowadays that doesn't matter as much due to most DVD players or disc drives being region free, but I recall the time when I was younger in the late 90's to early 2000's most discs were region locked based on where you bought a copy (basically the same as buying a Japanese N64 cartridge versus an US one) meaning they won't work when in another country.
For instance: I've purchased the first 2 home alone movies in Japan during my trip back then when they're re-released on DVD (encoded as NTSC) while I come from a country where most discs by default are PAL so they didn't work on my normal DVD player, having to purchase a multi region DVD player just to watch them. (This was before streaming sites).
Australian dollar is a weak currency for international travel I've heard, as the exchange rates are always lower than referencing from USD (like for example, A$1 = 0,60€ making it expensive). Like not all countries accept AUD at face value while USD is literally recognized everywhere.
Basically, they would have to pay more. Don't even talk about currency exchange with AUD, as you will get less than USD holders, for instance: A$100 = 60€ while $100 = 87,20€ (A$146), which is why refrain using Australian Dollar for international travel (just bring US Dollars instead).