I would say that's only usually true, or at least it comes up enough in Dungeons and Dragons to feel like it. Good, well-designed rules, when used with the correct understanding of what kind of fiction they're trying to produce/emulate/whatever, should not have cause to supersede the fiction. The Fiction and the rules should mesh, if the game is well-designed and the game book is well-written.
To be clear, I think that the reason I like the phrasing is because we often think of the rules (here, written rules) as establishing the fiction. However, supersede is a more meaningful phrase. It doesn't just establish fiction- those written rules, whether they are good or bad, whether they match the internalized fiction or not, supersede the fiction.
You might say that certain games, in having a very narrow scope, create less dissonance (which I think is true- I also think that FKR games usually work best when there is an agreed-upon, and narrow, scope). But the entire point of written rules is, to the extent that there is a mismatch at any time between the rules and the fiction (the internalized fictions), the rules supersede the fiction. You might even say that this is the point of the written rules.