Oh, absolutely! I suppose I've only been talking about games that are. Even for games that aren't skill-based, though, I'd question the value of adaptive difficulty... If your game isn't about skill, is there a reason to have a significant enough skill component in it that it might need to adapt downward to accommodate some players?
exactly. if your game isn't supposed to be challenging it's probably better to just get rid of the concept of "difficulty" altogether.
on the other hand:
Maybe I'm drawing too hard of a line between "challenge games" and "experience games", but thinking about it, I really would consider them totally different animals. Would Gone Home have worked as well if there were some skill-based challenges interspersed with the exploration?
it would have been out of place in gone home, but la mulana and the first legend of zelda are hard exploration games that are pretty damn great. challenge can be part of an "experience" i think.