Internet "boycotts", especially when it comes to video games, are largely ineffective and ignored by publishers and developers. Boycotting L4D2 is not going to keep it from coming out, nor is it going to keep people from buying it. As many people have said, even people boycotting the game will probably buy it anyway.
There's a slight variation on this for PC gamers. I was a hardcore PC gamer for a long time, and I can tell you, they operate differently than console people. Valve has been the darling of the PC gaming community for a long time. Steam was originally viewed as a misstep (because it REALLY sucked at first), but it was a small price to pay to play Half Life 2, and it improved rather quickly. Other than that, they've been golden. However, if PC gamers start thinking Valve is going more console-centric, they'll quickly abandon the company and move to a developer that DOES seem to have the PC in the forefront.
Perfect examples: Crytek, iD, and Epic. As I was leaving PC gaming, all three of those companies had pretty much fallen from grace in the eyes of PC gamers. Crytek's Crysis basically didn't run well on ANY of the existing hardware at launch and seemed very unpolished and unfinished in later levels. iD's execs were all talking about consoles in interviews and how they're going to start focusing more on them. Epic was kind of the same as iD. The same thing could happen to Valve once they realize there's a lot more money in consoles and start using the PC as an afterthought.
This is the natural progression of things. Developers do great things on the PC, they get big, they move on to consoles, and new developers come to take their place.