The map on
this link shows the following discounts:
Asia: "up to" 25% off
N America: 15% off
Africa/Europe: "up to" 40% off
Australia and S America are blank, but probably follow N America and Asia respectively.
There is no list of non-participating hotels, perhaps because "up to" includes zero discount.
A brief look at some Australia hotels shows the rate is available sporadically but is worse than the usual advance purchase rates.
Last year's "Any Weekend Anywhere" deal was quite good for Australia, but looks like it's rubbish this year.
As for 15% off the Best Available Rate for N America, for a prepaid non-cancellable rate, that's not going to attract a rush either.