> It taints the perception of the game beforehand. People look at an incredibly raw bit of gameplay footage and go "wow, this looks like trash!"

I'm not saying you're wrong, but I have to say I'm surprised that people would think this. Looking by analogy at big Hollywood movies, movie studios often release their own "behind the scenes" video clips, and as far as I can tell, these clips aren't generally considered to detract from the finished movie in anyway (and I personally find them, and this GTA leaked video, fascinating)