gorice
Hero
Regarding your first paragraph: to what extent is a rule non-structural because some people don't follow the rule? No game designer can make players do things by the book. I think there's a difference between a game that people play 'wrong' in some instances, and a game that people play 'wrong' in most instances, or a game that doesn't have an obvious 'right'. This is all possibly a matter of degree, to be fair.It might be my fault for not making it clear; I'm talking about the structure of the system. While resolution approaches are not completely disconnected with that, its far more vulnerable to, from lack of a better term "local conditions"; no matter how a game describes how you're supposed to approach dealing with particular types of problems, people will use the core mechanics in other ways to do that. That comes up outside the D&D sphere too (dip into enough threads about PbtA games and its abundantly clear a non-trivial amount of GMs ignore the way they're told to use the system, sometimes in ways that seem kind of appalling to PbtA proponents, and PbtA games and related have always been far more rigid in that way than virtually any editions of D&D.)
As such, I don't think a lot of things that are theoretically part of a game loop don't seem particularly core to people because they've played in a lot, maybe all their games that don't follow it. But they've still probably played D&D with classes, levels, level elevating hit points and a couple other things. Its far more central to the overall D&D hobby than any specific playstyle (though there are certainly some styles that have been very common throughout its history).
The more important question is: if everyone plays with classes, levels, and ascending HP, does that yield some kind of 'core' D&D experience? I would argue that it does not, and point the the incredible wealth of D&D-derived games (including video games) that all contain those same elements, and yet play very differently.