I didn't read that as implying everyone would be publish to Steam. In the context of related comments from Valve, I believe they're considering allowing others to more easily use the Steam distribution system to build their own storefronts.
This would allow third parties to create their own Steam-like stores, built on Steam, collating games from whoever submits them - imagine Humble Bundle, or a store that exclusively sells 3d platformers, or a publisher with a storefront with only their own games. Valve could still pick games out of these to put them on the official Steam store front. Plus Valve still gets a x% cut of each sale.
This would allow third parties to create their own Steam-like stores, built on Steam, collating games from whoever submits them - imagine Humble Bundle, or a store that exclusively sells 3d platformers, or a publisher with a storefront with only their own games. Valve could still pick games out of these to put them on the official Steam store front. Plus Valve still gets a x% cut of each sale.