Hardcore pirates will always find a new excuse, but well-implemented DRM is really helpful at encouraging mostly honest people to be as honest as they believe themselves to be. A huge segment of the population will be every bit as honest as you require them to be.
Within many game companies, the goal of DRM is to prevent people from pirating the game for the first week or two. They know better than anyone it'll be cracked eventually. But DRM definitely has an effect on sales if the pirates have to wait a few days to get the game for free. At least some of them will pay, if they have to.
