Some people on YouTube play entire video games start to finish without even adding any kind of commentary. On the other end of things, you have things like some of the stuff mentioned in the article, or that TotalBiscuit/Garry's Incident blowup in which a company was clearly just trying to squelch negative reviews. The latter is clearly fair use, while the former is at best a very grey area.

While there are some games where videos are clearly not a substitute for playing the game (puzzle games, multiplayer games), there are others where they might be (low-difficulty games with a lot of FMV cutscenes)