From what I've seen and read in this thread, it's a kind of adult sexiness. It's more about seduction than about actual sex. That's why I say Versailles and Helmut Newton, to me those represent a refined kind of eroticism.
Anyway, I do agree with what many have said, that this is hardly new for fashion, but it has been a while since designers were showing something sexy on the runways. But, I think in a way it is a "trend" because so many designers, including those who aren't really known for it, are taking various "erotica" touches (like garters, stockings, platforms, sheer fabrics....) and using them in their collections to create a polished sexuality.