Any taken revenue is stolen revenue. These people are creating something new out of the games they play. They are not streaming the game per se, they are streaming their play through of the game. So long as they are not distributing the game in end of itself, then the company has no business taking money from it. The only situation where I could see a gray area are David Cage "games", but then again, you know how I feel about weak movies with button prompts.
The only reason Nintendo is taking money form these people is because they know they can't fight back and they can control their message by holding their career at ransom.
Furthermore, Youtube already takes 50% of the revenue.
So Youtube takes 50%
Nintendo takes 30% of that remaining 50%.
You must go through paypal to get your money, so they take a cut.
If you are not american, you must pay extra fees to convert into your dollar currency.
You essentially loses more than 30% from Nintendo actually.