Not to deny that Greenlight is important but that seems to be overstating it. There was lots of buzz about Papers, Please back when it was still just a free-download beta on Lucas Pope's website; now it's on not only Steam but also GOG and the Humble Store. Of the notable "indie" hits from the past 3-4 years, most were probably (or certainly) in development before Greenlight was even announced, several got on Steam without going through Greenlight at all, several were successful on other platforms before going onto Steam (Amnesia, SpaceChem (initially rejected for Steam) ...) and some have kissed off Steam completely (famously Minecraft). If anything Greenlight looks a bit like Valve's late entry to the Humble Bundle/XBLA party.