I think whether or not this happens comes down to who is hosting the content. Sony sure as hell ain’t gonna do it for free, and while the two obviously worked out a pretty sweet deal, I’m not sure Sony is willing to give up enough control to allow Valve to distribute whole games from the Steam server. I figured it would just be an updates and patches type thing.
The one thing I’m fairly sure of is that IF Valve is allowed to give PC buyers the PS3 version for free, they’ll do it.