They seem to have modified the deal. Now you get a single use coupon for 15, 20 or 30% depending on how much you spend. However, they make it appear that only books on a short list are eligible for either buying (to earn the coupon) or for redeeming the coupon. I know they always had a list of titles for other discount coupons but the sale applied to all non-agency books, so perhaps the same thing is true again this time.
Of course, it's more difficult to find a non-agency title as more publishers join the agency bandwagon.