I was happy to hear that Left 4 Dead 2 will include a sort of hardcore mode. Players can opt to give up aid from the interface, like being able to see one's teammates through walls by a surrounding glow.
Hardcore modes don't please only the hardcore. They also please casual players by getting hardcore players the hell out of their games.
For a casual player, there are few things more annoying than a fellow player trying to squeeze your every action into some achievement fanatic's model. It's like all freedom of choice is robbed from you as a tyrant barks out a strategy that he grabbed off some website for people who are more concerned about being the best than having fun.
I'm really not trying to insult hardcore players. I realize that winning is the definition of fun for some people, and that's fine. I enjoy victory and competition, myself, but I'm generally more concerned with the journey than the end; as are many gamers.
I'm just pointing out that providing a hardcore mode or customizable multiplayer scenarios allows hardcore and casual players to each enjoy playing the game their own way. A hardcore mode can be a good idea even if the hardcore are not a major part of your target audience.