The slums, the poor, the grinding poverty thereof. (It didn't come up that this tends to be sword & sorcery, if I remember rightly.)
The selective use of realism to include such salacious details as appeal to the writer, or his intended audience.
A Game of Thrones came up, surprise. Too much violence for their taste -- and one panelist objected to the notion that no one could kill Tyrion, who's only a dwarf. I think this was the panel where two panelists objected on the grounds it lacked gender equality. They were willing to concede that it could be allowed in a historical setting but that in an imaginary world, it was required, and they wanted it. (I thought, but did not say -- did not even try to -- that what occurred historically is a legitimate think to base your world-building on.)
Hmm. Come to think of it, magic and how it impacts mud and blood would be a major topic, but it didn't come up, and I didn't even notice. Perhaps I shall write on that myself.