The conspiracy theorist in me says : Giving a developer money for using Steam would be good for me as a Steam holder, because it would further harden and strengthen Steam's position. If anything goes well, even into a kind of Monopoly (that would be ideal, because then, Steam could dictate prices over developers in the long run, too).
There are rumors that Valve would develop their own console. Wwell, that would mak perfect sense. Because of Steam, which is nothing but a variant of
- Windows Marketplace
- App Store
- etc.
Since consoles and iDevices are "closed environments", a Steam console would be ideal to dictate pices. Plus, if people HAD to buy a "Steam Console" in order to be able to play games listed on Steam, it would put some sort of pressure (maybe even peer pressure) on those who wouldn't have access to Steam-games, then.
From a capitalistic point of view, a Steam Console would make perfect sense, because it would be a special kind of Monopoly for the PC markt, simply because there doesn't exist any "PC Console" yet. There are XBOX, Playstation etc. - but not a PC Console yet.
And that would put Valve into an excellent position.