Are you being intentionally obtuse? Some excellent games may not have a crazy social networking fanbase paving the way on Greenlight.
This sort of stuff also encourages things like vote trading and weird emergent politics.
To me it doesn't make sense to have Joe Public evaluate games well before release. Some concepts are hard to communicate and this sort of stuff really favors games that have some obvious hook or are in a well-trodden genre than games that don't reveal how fun they are without playing them.
The same is true of Kickstarter to some degree, the games that do well there are mostly retrograde nostalgia plays.
It's also just kind of depressing that it's getting to the point where to be a successful indie game dev you have to be a promoter/marketer first and a game maker second. I get at some point to be successful you need some buzz but we're quickly reaching the stage where if you are making a game you're going to be spending much of your time making cloying videos, updating websites, lobbying for votes in social media, etc, even in the very early stages of the project. It also encourages over-promising.
Edit: Looking at the list of greenlit games I see a lot of Zombie games and Minecraft clones. Same shit as what's popular on XBL Indies. I really don't want troglodytes who only vote up games because they seem exactly like games they've already played determining what's on Steam.
There are lots of awesome things the public doesn't know it wants until it gets it, and if you ask people what they want they'll most likely riff on whatever is hot.
