As always, ebook retailers can only offer these discounts on ebooks from certain publishers so they won't work for all ebooks. (blog.the-ebook-reader.com)
I can remember when I would browse the shelves at bookstores, looking for the logos for certain publishers. (madgeniusclub.com)
I was just pointing out that some authors didn't have a choice because of contracts with certain publishers. (goodereader.com)