Ninty isn't getting nothing. They get free advertisement.
Free advertisement = more units sold = ??? = Profit
thats what they said about pirating pc games way back when too. same thing with music pirates and people playing music on parties (which is basically illegal, same as having a dvd evening with more than your closest household members).
be honest, a lets play is on a whole different level than lets say, a fan review or someone making vids like the videogame nerd. advertisement is short and doesnt require the whole game to be showcased.
irregardless of lets plays actually having any advertising value at all, it remains a fact that nintendo has every right to be against them or require monetary compensation for them. if sony or microsoft dont do that, its their loss (though I'm pretty sure they too, have some rules on lets plays)
So why then do other companies like Ubisoft, Sega, Sony, etc not have any beef with those who upload content? AFAIK, Sega doesn't mind people doing it at all.
because they believe that the gains outweight the losses here. its pretty simple, no matter how you look at it, the effects of lets plays on sales cant be measured. it can only be believed in.
it sounds like a nice little theory that more videos on youtube mean more sales of a game. but its nothing more than that, a theory with no proof and no way to prove it. and honestly, it goes along the lines of 'piracy and hacking give new life to a console'.
personally, i believe lets plays to have either no or a negative effect on sales, while reviews have either no or a positive effect (in case the game gets a good review that is). that is because the lets play offers the watcher the whole game, every storyline element, every plot twist, every battle and every boss. all it withholds is the aspect of doing it yourself. which is a noissue for most people, if you watch a whole lets play it stands to reason you either have the game already and want to know how good or bad you do compared to someone else, or want to learn a few tricks and secrets. or you dont want to buy it / cant play it due to lack of console, but want to know how it is and what happens so you can talk with others (which is what half my brothers class does. they all have an opinion on most ps4 games, while only two actually own said console).
while the review only gives people an overview, a few good and bad points and a personal opinion. pretty much what every add on tv and all other media has been for the last few decades. a tried and true formula. because if all you need to buy is an advertisment, you dont need 25 hours of gameplay footage.