I'm not sure if you're all aware, but Amazon is once again throwing it's weight around when it comes to publishers and the books it will carry. This time the dispute is with Hachette Book Group. There are always disagreements between retailers and publishers. The publishers want to make a profit on of their product, and the distributors do as well, but also want to be competitive with other retail outlets for said product. That means, usually being the lowest priced. When it comes to Amazon, you'd be hard-pressed to find a bigger retailer, especially when it comes to books. This is what makes it such a difficult situation for everyone involved, when the two sides, retail and publisher, cannot find common ground that works for all.
Below are some articles by people far more intelligent and grasping of the situation then me. For a quick overview, check out the L.A. Times article, I found it to be the easiest to understand. The School Library Journal article is pretty comprehensive, and then of course I have the three articles with some big names (John Green, James Patterson, and Malcolm Gladwell; the latter two are actual Hachette authors) speaking out against the situation. Then for funsies (and for serious), Stephen Colbert (who is also a Hachette author) brings the situation up on The Colbert Report which witty commentary.
Amazon and Hachette: The Dispute in 13 Easy Steps (L.A. Times)
Authors John Green and James Patterson Stuck in Midst of Ongoing Battle of Amazon vs. Hachette (School Library Journal)