Target stops selling the Kindle

Target announced that it will stop selling Kindles and other Amazon-branded products, but will continue selling Barnes and Noble's Nook. Admittedly, Amazon doesn't help brick-and-mortar retailers out too much by undercutting them on price, but I'm still surprised by Target's move here. If someone wants to buy a Kindle in a store, shouldn't Target be willing to take their money? I can't imagine Target does a big business selling paper books, so what's the harm?