for the most part I too think PAL is PAL the only reason I originally asked is because of the controversy back at the time that meant that this game was limited with Australian Ratings etc.. (much like the US version of SMS Sonic) either way I still think it is one of the less common things that I own in my small collection of stuff.
Price tag is irrelevant. The main reason I have come across is that the "Australian release was limited" - the only thing that justifies this view is the fact that our population is so much smaller so it's obvious there are less items delivered and sold here. Either way though, some of the prices seen just because it says AUS is ridiculous, and the price fluctuations are testament to showing the pricing (and often, shill bidding) is incorrect. Some Starcraft copies went for $1000, now they are getting $400 and that's a change in a couple months! Personally, I hope the prices drop. I can understand a rare title exclusive to AUS only having a higher price second hand though.
Starcraft 64 (which I assume you are talking about) was a rare exclusive to AUS in PAL release. Some snes games that didnt get local versions to NTSC or PAL fetch insane amounts as well Terranigma and Super Mario RPG are the two big ones I am familiar with.
RRP does somewhat play a role in the second hand price, it depends on how much they sell. Secondly like you said the population. During the 90's many people didn't play video games like today. Regardless prices here for games are stupid, and there are deep pocket bidders on eBay Australia, eBay is my last resort for anything at the moment. Prices won't drop unless sellers fix the market with BIN prices. I've been knocked out of auctions left, right and centre for XBOX stuff lately. It's those buyers who ruin the market because once one items sells for way more what it's really worth, the next one will show up around the price and it snowballs from there.