Hmm, I think every creator would feel put out by someone ripping off their work, and it would be generally a communal standard that not crediting someone else's work is a shitty thing to do.
I think it might be better to ask 'how specific does something have to be in order to feel justified in feeling ripped off'? Like for example, if someone used like some of my very broad and vague ideas, I don't think they need to credit me, and it probably wouldn't be reasonable for me to get annoyed by it. Like Arx's random scenes, first impressions, very general design and incentives are pretty simple, general ideas that I think anyone could come up with independently, and I don't think I can feel particular ownership over them. On the other hand, if someone lifted the actual code without asking or giving credit and used it, that moves from general ideas to work, and that would probably make Tehom annoyed (even if he would have said 'sure' if someone had just asked).
Put another way, one person had to be the first one to decide that a wiki to go along with a game was going to be a great idea, and enrich the RP experience of a lot of players. That's a general game design idea that just became a largely agreed upon best practice, resulting in most games using wikis, and I certainly have no clue who the first person that had that idea was. But ripping off the specific formatting code on the wikis moves past the territory of best practices to stealing someone's creative work. And I think the line between the two can be a little vague sometimes.