After hearing from people on the inside at Amazon, I am convinced it was in fact, a "glitch."
Well, more like user error—some idiot editing code for one of the many international versions of Amazon mixed up the difference between "adult" and "erotic" and "sexuality". All the sites are tied together, so editing one affected all for blacklisting, and ta-da, you get this situation.
The CS rep who responded that this was Amazon policy was just confused about what they were talking about, and gave standard boilerplate about porn.
The dumbest part is saying it was a "glitch". A "glitch"? Just say that it was one of your workers making an editing error. Really dumb PR move, that one.
Let me know if you actually want more details on how it went down, but it's pretty boring and technical.
I asked Mike for more details, and according to his inside sources, the story is that a programmer at Amazon France was editing the site to filter porn out of some search results, and he "mixed up 'adult,' which is the term they use for porn, with stuff like 'erotic' and 'sexuality.' The system he was working on is universal, so the change he made propagated across Amazon's sites worldwide.
Amazon's systems are notoriously idiosyncratic so it's not hard to imagine a change like this getting into their worldwide system, though it's certainly interesting that it would be so difficult to correct the problem.
When Mark Probst received his reply from customer service, the rep misunderstood the problem and sent him a boilerplate response on how they deal with "adult" content.
The technical reasons for this glitch (no quotes!) are still hazy at best, and it seems increasingly unlikely that Amazon will issue any sort of real explanation, unfortunately.