No, what I mean is when a writer goes to tell a story, often retelling a story, in, say, a SF future. The problem is that the social hierarchy required is not -- futuristic. Indeed, it's rather more often seen in the past than in the present. Or perhaps it requires that there be servants.
One can take the tack that whatever has happened can happen again, and glide over the issues of how, but that can produce a rather thin world. The problem is that there's a real danger that the explanation will take up so much of the story as to crowd the actual story out of it, and take up too much of the reader's interest. If the story uses robot servants, and these servants act entirely human-like -- necessary for them to take the plot place of human servants -- there is the little question of why they are subjugated, and what they think of it, and what the human characters are like to allow this. Or how the aristocracy came back and managed to install itself in an industrialized world, and how it keeps it going and keeps the technically educated lower classes -- probably necessary -- in their place. (More or less, depending on how permeable the aristocracy is.) And how the laws got changed in either of these situations to conform to the consequences.
Regardless of what the world-building is, it's always possible for it to hog the reader's attention. It's hard to tell a reader that "this here bit is just local color, and you're not supposed to care about it." (My own coping mechanism for when they throw something away like that is to steal it for my own use. 0:) And readers of varying interests will wonder about varying aspects of the world.
Still, it tends to get an annoying twist in the social structure aspects. There is always the reader with the Whig interpretation of history who doesn't want to broaden his mind and read about people who live -- and think -- very differently from him. Who thinks that the only legitimate use of a non-egalitarian society in fiction is to debunk it for a democracy. (Sometimes, for added irony, he doesn't want exposure to people who think very differently from him in order to protect the purity of his broad-mindness and tolerance from their taint.)
