Any youtube thing is weird. It's all very middle ground and not quite one way or the other. No matter how much you argue that it's free advertising or anything else, doesn't mean it's not hurting a developer if people prefer to watch a game being played so they don't have to buy it. Yet, the 'free' advertising does work, I bought BL2 based on youtube videos (I bought it used so a bit of a waste in reality but still :P).
There is an issue with this though, it's the 'free' part. People are making money from other people's work. No one would stand for a youtube video where someone read out a book they bought chapter by chapter and had adverts on with no money going back to the writer. Would people argue 'But they've bought the book, what is the problem?'. The problem is this person is making money from someone else's work not their own.
All Nintendo did was ask people not to put adverts on their videos, right? Yet people took this and no videos at all. Not sure if this has changed since but this is a great policy. That PewDiePie or whatever his name is is currently making millions a year now on his videos. I wonder if any of the developers of the games he plays makes nearly as much, I'm not talking about the big company like MS, just the 1 or 2 developers who wrote their indie game.
Hmm, pie.
