Valve met with Notch at the peak of the Minecraft hype a few months back, and they failed to secure any distribution rights, as they receive 30% of all sales and this, along with the fact that they are /the/ digital distribution platform that everyone goes to/they have a monopoly, brought Notch to turn them down.
They met no resistance when they approached the developers of Terraria, Red and Blue, whose product had zero-marketing save for dinky webpage, a YouTube trailer, and a mention on Notch’s Twitterfeed, and scored the rights to be the sole distributor of their product. The game opened on May 7th to an estimated 50,000 sales at $9.99, and has been one of the most actively-played games on Steam since its release.
As of the last patch, the game can no longer be launched when offline. I’m not so sure how I feel about Valve right now.