Don't know if Roc is imitating Gollancz, but it's the second time in the last couple of months (the first title to be offered at such a discount was Guy Gavriel Kay's Under Heaven) that one of their books can be purchased so cheaply.
At the moment, the #1 New York Times bestseller Changes by Jim Butcher (Canada, USA, Europe) can be bought at 58% off on amazon.com and at 49% off on its UK counterpart! Nothing of the sort of Amazon's Canadian site. . .
So if you wish to purchase more Harry Dresden adventures on the cheap, now's your chance!