I've been thru Apple's review process enough times, and been rejected enough times to say that Apple does apply its rules equally.[1] Given the responses I've gotten back from the reviewers, it is clear that I've interacted with multiple reviewers, and I've never seen a deviation.
There is the occasional mistake, but the very telling thing about this article is she never tells us the specific rule that she broke. Hiding this information is important for making it look like Apple is arbitrary.
But the thing is, when you're rejected by Apple, they cite the specific rule.
Since there are lots of books about Amazon in the bookstore, and since there is no rule against publishing books about Amazon, this story does not add up.
[1] Every rejection resulted in me immediately getting pissed off, much like the original OP. But once I calmed down I realized either I misunderstood the rejection, and the fix was easy and the rejection was legitimate, or the rejection was due to me making an error that would produce a bad experience for the customer, sometimes because I misunderstood the guidelines, occasionally because I was being lazy without realizing it, and often just because of a mistake or bug.
Since Apple is uniform in the way they apply the rules, and the rules are not so specific as to cover specific bugs, it does take some interpretation to figure out what they are saying. If you don't take that step, its easy to fly off the handle and assume Apple is being arbitrary when they aren't. The reality is, it just means you didn't take the time to read what they wrote you and comprehend it.
Of course the rejections feel personal, and I won't tolerate a company that won't play by its own rules, but they've never been unfair to me, and other than a few mistakes that were corrected, I'm not aware of them being unfair to others.
However we get a lot of these kinds of stories where someone says one thing, but they never cite the specific rule, or are evasive, which indicates that they're just trying to get publicity and were really rejected for other reasons.