Did I miss the part where Youtube has become an emulator for me to play games on, or a server to download games from? Because that's the only way Youtubers would be in direct violation of piracy laws. What they're doing now is creating content on their own using software they paid for. You don't see Adobe suing people because they make videos of people making art in Photoshop, because they don't own what you do with the software. Similarwise, developers have no claim on the gaming experience of people, and that's what Youtube videos are about, an individual's gaming experience which varies for every person using the software.
To give an example, the only Youtube gamer I follow is Robbaz and while he does playthroughs of some games, what makes his videos awesome aren't the games he's playing, it's how he plays them. And while the popularity of a game might influence the popularity of the video, in the end he is the one to sell it because there's thousands of playthrough videos that don't get as much as a 1,000 views, let alone the millions that probably don't even get 10 views.
If people just wanted to see the game content, they could watch every "Let's Play" on Youtube. It's how these gamers play the game, the commentary they give on it, that ultimately sells the video, not the game and sure as fukk not the developer.