This was inevitable. I don't think people here realize just how much money you can make from YouTube and Twitch.tv streams if you're popular.
What's going to happen here in the future (if this isn't cut off at the knees, now, and I'm not sure streamers have a legal leg to stand on, any GAFLaw in the house?) is the bigger publishers are going to sign exclusive agreements with companies like Machinima and forbid any other streaming/commentary videos outside that single outlet. For streaming, that's mostly twitch, but there are other streaming sites out there that could become competitors with an 'exclusive' agreement to stream GTA5 or whatever.
Companies like Machinima and others stand to make a huge amount of money if they can score an exclusive agreement with a publisher for a huge title, and I seriously doubt that the guys actually generating the content (ie, videos people want to watch) are going to see even a fraction of that money. Sorry proles, suck capitalism
Needless to say, as a streamer myself, I'm no fan of this whatsoever. My viewers largely tuned in to watch
me play, because of my particular style, sense of humor, presentation, etc. This was true across many games, not any single game.
But again, legally, I suspect they hold the cards, as full videos on YouTube that are monetized are probably well past fair use. I don't know about streaming, but I'm assuming it falls under some sort of rebroadcasting for public use laws.