Name one expansion for an FPS type game that changed how the game play is. An expansion is usually what they already had in the game (or what they didn't feel worked right with what they had) and said it would work better if we sold this for $20, not a reworked game code to fix things and change game play they were not expecting for that would take quite a big fix.
Please, complain more, I personally won't be missing you when I'm playing L4D2, a completely different game, not an expansion. You would be lucky to get even that for free from other companies. I have no doubt in my mind they will keep releasing DLC for free for L4D, and not because of the boycott, because of their actual fan base and not people who want free things from a company that goes beyond the call of duty. They updated it fixed problems, added a new mode, added more versus modes, changed game play for versus from what people have complained about, and countless other things.
They released a game that got a 89 on meta critic, 89 isn't half a game. Uhm, 'They promised us DLC! Boycott L4D2 because it should be an add-on!' ' They made DLC, they only made it because we moaned.'