Rilus: You are correct about sierra not giving valve a penny to develop the game, but sierra is fitting the bills of promoting/manufacturing the game.
Promotion of a game as big as half-life 2 is not cheap. They were stupid to agree to let valve independently distribute games independent of the publisher in the first place.
Because if vivendi spends 2 million on advertising and valve spends zero, valve is freeloading of sierra's advertising and valve and sierra become competing intrests. (IE with one cmpany having online distribution rights and the other only physical distribution rights.. things can get nasty...).
This one will be iteresting. Steam is fine and all, but it should be handled by the distributer, (steam's main purpose is the 'distribute' the game), and not the developer.