That middle photo looks like it came from Awkward Family Photos.

I'm sure sex can help sell themes. It sells just about anything else. And sure it can be inappropriate for a younger audience, but have you watched TV in the last decade?

I personally don't think it's been much of a "problem" with themes. At least, it's pretty low on the list. People can put whatever they want in the demos for all I care as long as the themes have decent code. But alas, that's asking a lot I guess.