I'm intrigued by where that line is for others. What makes a novel "realistic" for Jane but not for Bob?

I think now you're getting into sociology and psychology! I think readers need different things from text -- and so, just like with anything else, you'll find some texts that seem to have an almost universal appeal because people can fill in the blanks in the ways they want to (or because the blanks are filled in in ways that appeal to them)... and some texts only appeal to a niche market, because the blanks/unblank bits don't have the same sort of "universal" resonance.

Does that make sense?