Still have to disagree with you.
They can have a vague "no objectionable stuff" rule and decide on an individual basis what constitutes objectionable stuff
to them. It may not be objectionable to me or to you, but if they deem it so, then it is so
on their site. There is nothing that requires them to apply any consistency in what they consider objectionable. Again, we might want them to do so, but they are under no legal obligation to treat what they might consider pornography in a consistent manner.
They are marketing to different locales, different countries, where attitudes toward sex and the public depiction of it differs widely. They are in the business of making money, not being harbingers of change. They've got to sell what can make money for them, and yet not cause them to run afoul of the anti-porn crowd and hurt their sales. And frankly, the public at large is not going to get worked up over Amazon putting limits in that area; all that's needed are a few parents complaining to the media that Amazon is selling porn to their teenagers and watch what a sh*tstorm will occur - a much greater one that folks here crying discrimination.