This is just one specific case out of the many, many organizations and individuals publishing content on Apple's iBookstore, but it's an interesting call by Apple nevertheless. Seth Godin tried to publish a book of his through Apple's iBooks, but the content was rejected by Apple's system. Not because it was offensive in some way, but simply because it contained links to Amazon's booksore. These weren't even links to Godin's books -- they were simply links to reference books, but because they went out to a competing service, Apple pulled the plug.
Before anyone starts yelling about censorship, keep in mind that this is Apple's playground, and it can take its ball home whenever it wants, no matter how inane the reason. But this reason seems particularly inane -- Apple can't really be worried about one link in a ebook promoting a competitor's sales, right? Not to mention that the book in question was a hardcover copy, and unless I'm mistaken, wasn't even sold on Apple's iBooks store anyway.
Apple's staked a claim to be at the center of technology and creativity, and of course it's done plenty to cement a spot for itself there. But education and information are a key part of creativity, and if Apple is openly choosing to shut down certain purchases on its stores just for the petty reason of trying to keep one or two sales away from a (sort of) competitor, that's a mistake.