According to that quoted text, if they notify you of the cancellation, then they are entitled to cancel items that end up being more than they had it listed for... which will happen if they Australian Dollar keeps slowly strengthening against the US Dollar.

This is one reason I rarely pre-order items that are a loooong way from their release, especially regular release items (like the Kingdom and Studio Series toys that are due out March to June, but were being offered for pre-order in September-November last year).
If it is a pre-order of a US item that is more than a month away from release, perhaps order the item through the US site and just pay the shipping to improve the chances of getting it... and it still might end up being close to the Australian price at the time of release, as a better exchange rate would have made it cheaper.