Nintendo and Youtube.

I wish I could explain it better, but unfortunately, I'm not smart enough.

Basically, it has to deal with the rights gained when buying software. You now own that specific software. You can do whatever you want with it, barring redistribution (as that's specifically against the law). When it comes to uploading videos of recorded footage onto Youtube, it's not against your inherited rights from buying the software in question, so long as it doesn't fall under the aforementioned circumstances.

Ah, but you are redistributing parts of it. Specifically the images (and probably music). This is in part why most Nintendo games (and probably nearly every game) at the end of the credits say something along the lines of "All rights, including copyrights of Game, Scenario, Program, Music are property of nintendo".

Simply uploading a rip of the game files isn't the only way to redistribute parts of the game which (Apparently) legally belong to nintendo, whether you own a copy of the disc or not.

I'm not arguing it isn't a plantain move (absolutely is), but still, like everything, the goal of a publisher is to get as much of your money as possible while actually given you as few rights as possible.