Nintendo and Youtube.

But it is plausible that at the end of the day they turn out with less money because they lost this free advertising of let's play. Therefor attempting to gather more money, yields them with less.

Maybe. But I seriously doubt it. I'm probably a bit biased because I've never watched a lets play and then gone out and bought the game, while I have been prevented from buying a game BECAUSE i've already watched a lets play of it.