"Valve and Sony" are apples and oranges. Valve hasn't been a publisher (in the usual sense) or a platform creator until very recently. They've been a retailer and a developer. As a retailer, Valve has an incentive to grow the industry as a whole, and as a developer, they have an incentive to get people onto platforms that are easy for them to develop and sell products for.

They've chosen to tackle these interests by deliberately doing things "wrong" right from the beginning. SteamOS/Steambox is all about having an open, accessible platform, and the release of development tools is all about getting people to develop for this platform so that users will adopt it.