It is probably a consequence of the favourable exchange rate. An app that sells for US$10 costs AU$13 here. Right now they get close to US$13 for each app sold

It is probably a consequence of the favourable exchange rate. An app that sells for US$10 costs AU$13 here. Right now they get close to US$13 for each app sold in Australia, but they still pay the developer a cut of US$7. That's a profit margin of 46%. Gift cards sold at 25% off simply bring Australian prices closer to US prices. Apple probably just offers these discounts as an alternative to continually fluctuating their internal exchange rate.