It would be a failure if they were a tool to make indie games more known ... but they are searching for more marketeable games and games that will likely sell more.
If you can't do the market for your game and people look at your game and don't want to buy ... than don't matter if you game is the best thing since Super Mario Bros.
I see a lot of comments about this, but I really think this is the absolute worst way to go about things in my opinion.
I am against the idea that devs need to drive outside traffic to their greenlight page. Yes of course that is important but there are a lot of pitfalls that people are missing when they say this.
For one you need to drive traffic of already registered Steam users in order for it to make any sort of a difference. They have a closed system in which only their paying customers can vote so it doesn't really follow logically that driving outside traffic will have a big effect. There are of course exceptions such as maybe advertising on a PC centric site like Rock Paper Shotgun or using synergy with a Kickstarter project as I believe there is overlap there.
I have personally handled a bunch of e-mails from La-Mulana fans who bought on WiiWare and want to help support the game getting on Steam. But they aren't Steam users so they have no say(people forget that yes Steam is big but it is still just a tiny fraction of the overall game market.) This could provide a nice large influx of votes for La-Mulana, but the system is closed so it isn't possible to make use of these interested gamers. Now I understand why the put the voting criteria in place and I don't think they should make it a free-for-all, but I do think that if they created a closed system based around voting then there is a responsibility to provide incentives and reasons for their users to participate.
I just see a large disconnect between making a completely closed system where only Steam customers can vote but then expecting the developers to provide outside traffic.
There is also the fact that no one can keep marketing at full capacity forever. It just is not possible unless you have bundles of cash as interest will fall off and consumers will forget. In my opinion that could be money better spent on marketing the product when it is actually available. I know it isn't a really popular position and most people will just reply with the likes of "damn indie amateurs expect to get rich overnight with no work" etc. but I think Steam needs to do something to drive interest in their own service.