Just a thought: the downplaying of adult literature may have little to do with the stigma attributed to the category itself. It is unwise for a company that serves a broad base of customers to appear as though they serve a paricular base of customers. Imagine what would happen if a bookstore's sales were dominated by SF&F, and their search/rating algorithms reflected that. A lot of people would look for another vendor, one that better reflected their tastes. Or imagine a clothing store in a mall that only had women's clothing in the display window, even though the store served men and women, just because that sold better. About half of your potential customers would walk straight by because they think that the store is geared towards someone else.

Now I don't know the real reasoning behind these tweaks. It may very well be social stigma. On the other hand, I find it just as likely that other factors are entering the mix.