Valve, according to PC Gamer, gathered indie developers at a London bar to speak with them about some of the changes that Steam will be experiencing over the next few months. As with the upcoming Steam Greenlight, Valve as realized that it won't be able to attend to the ever-increasing number of updates and game submissions, so now they're taking a hands-off approach.
Developers can now update their games without Valve's approval. So if they happen to break the game, Valve isn't held accountable—the developers will, as it should be. It's nice having a middle-man that cares about the quality of the product, but ultimately it's not their responsibility to ensure that the developers are doing their job with quality assurance.
Established developers no longer have to wait for Valve to complete their testing. Without their oversight, though, it will make testing that much more important. The customers themselves will tell the developers if they experience bugs, and if they tell Valve about these bugs, they will simply forward those comments to the developers.
Also, by updating their games frequently, customers are notified via pop-up message that progress is being made. It apparently is a strong marketing tool, as the data shows that an update always brings a spike of interest and playtime with the title.