I don’t think it’s aboutGM authorship, so much as what prompts the GM to author something.
I think that’s the big difference in many games, and it can be difficult to notice. Especially in online discussion rather than in play.
Someone earlier (
@TwoSix I believe, please correct me if I’m wrong) talked about a GM framing a scene at a wizard’s tower because that’s what the GM had prepped, or framing a scene at a wizard’s tower because one of the PCs had a reason to go to the tower.
Of course someone immediately said “what’s the difference, it’s still a wizard’s tower”. But that’s just because of the nature of the example.
Suppose none of the PCs had any reason to be at a wizards tower? In that case, for many games, it would be poor form for the GM to frame a scene there. Not without some compelling reason for one of the PCs.
In many games, the GM is free to introduce such a scene by any means they like. Either because the hex the PCs have entered indicates a wizard’s tower is there, or because a random encounter table says it should happen, or because the GM had a cool idea for an encounter and wants to use it, or because the GM stubbed his toe last Tuesday.
It’s not THAT the GM authors elements and introduces them into play, it’s WHY they do so.