Left4Dead2 isn't a EA game, they are the publisher, not the onwers of the IP. Somewhat like M$ published Mass Effect, and then offered back the publishing rights to EA for ME2 to allow them to keep the game exclusive to the 360 on consoles.
EA is in EXTREMELY vunerable at this point, and imho, I think we might seem some shake-ups on the gaming landscape in the near future.