Warhammer Online designer Mark Jacobs openly posted in a thread stating that he wouldn't be distraught if he had to ship a game minus a couple of classes if it meant they could hit their target date.
And then, in the same breath (or whatever the forum equivalent of a breath is), he says that Mythic and EA are committed to shipping the game when it's ready, citing Blizzard's model for their continued success. It's all a bit confusing. For my part, I take more comfort in the philosophy espoused in the second post. As much as it would pain me if they did, they're not going to lose players by putting off the release date a month or two. You will lose players if they buy your game and find it is less than they were expecting.