I'd assume the fee for receiving funds through WeChat QR is significantly lower than the transaction fee for paypass in Australia, which might explain why so many stores have a minimum for card.
Fees for PayPass/PayWave on debit cards in Australia is 7.5¢.
Though, in general, if you accept debit cards in Australia you need to accept that network's credit cards too. My Visa Platinum is going to be more than 7.5c for most transactions, I imagine.