people kill me. how is adding options a bad idea. Valve didn't get where they are by not trying out things. not saying they should or shouldn't try this but its an idea nonetheless. Im glad people on this bored are not publishers. we'll have even more ideas thrown out the window.
See The Game Collection http://people.ign.com/nights_team2k7/games
The problem is they already give away stuff for free, so having a paywall will just make the already free stuff not-free. It's a bad idea. It was a bad idea when Sony tried it, and it'd be a bad idea if Valve tries it.