Well Kentucky Route Zero got through and that is one of the strangest most abstract things I've ever played, but it also had a very successful Kickstarter. The Greenlight experiment honestly does not work very well but Valve and Gabe Newell are totally aware of this. Gabe spoke at UT and addressed the very issue of how inefficient Greenlight is. It was kind of a first try at community sourcing games and it will be massively overhauled soon. For instance, right now Mutant Mudds which is well regarded as one of the better platformers of recent days is finding itself hovering around 50% approval which is insane. This is a proven game already that can't get approved because of the system.

I see no reason why Valve needs to ask every 12 year old that only is on Steam to play COD whether or not they like some strategic art game.

My guess is they come to some sort of Kickstarter-esque model where people will pledge to prebuy a game and when it gets to a certain threshold, the game will be Greenlit. Makes a lot more sense that polling every user on Steam, let the people who are willing to spend money make the decisions happen.