In the comments for my last post, Brooke calls me on an overstatement. It's really silly of me to in any way imply that nobody has thought about varying levels of commitment in your playerbase before now. Certainly it's a question that's been considered in the ARG community before. Sorry!
I think perhaps the reason I felt that way, though, has a lot to do with the beast that is the modern video game industry, and the inherently quiet nature of less-than-hardcore players. Let's look at that second topic first.
As Brooke pointed out, in any game there is a certain distinct body of fairly casual participants. The problem is that these people are difficult to keep track of. If a player in an ARG never emails a character, never posts to a forum, never comes to a live event, it's easy to imagine the player doesn't exist at all, no matter what evidence you might have indicating otherwise. Website stats are, after all, notoriously imperfect metrics. So when a design team is moving ahead, it's easy to do so based solely on the inherently more vocal hardcore base, who are talking publicly about where they want to see a game heading. How can one design for a group about which you have no feedback?
The big problem here, of course, is that the hardcore audience is not necessarily your largest -- just your loudest. And to be quite frank, the changes they want may be diametrically opposed to what would make the game more fun or accessible to an ever-wider audience.
Taking this back to traditional video games -- this problem of catering to the hardcore audience over the more casual gamer is very much to the point right now. Let's think about the next-gen consoles for a moment (I bet you didn't see that one coming!). On the one hand, you have the Xbox 360, clocking in at $400 and more without games. It's the baddest, most polygonrific system out there, right? More realistic textures? Yeah, sure. But this is a machine designed by the hardcore, for the hardcore; and I feel this is a pretty big mistake from a business perspective. The quiet body of gamers who want to have a fun gaming experience but don't want to commit thirty hours a week to it probably don't want to commit $400 to their five-hour-a-week habit, no matter how beautifully the water ripples. After all, how much more fun are the actual games? (What's that, you say? It's the same games?)
Nintendo is going against what one might call the siren call of the hardcore player. If I may be trite for the rest of this sentence; Sony and Microsoft are at war for a bigger piece of the pie, but Nintendo is trying to make a bigger pie, by designing specifically for the soft-voiced masses of the non-hardcore gamers (or even, in some cases, non-gamers period). For a really terrific (and even inspiring) summary of their Revolution business strategy, read this painfully all-caps transcript of a talk by Reggie Fils-Aime. This, my friends, is why my money is on Nintendo.
So, in summary: Certainly a lot of sharp brains have turned their attention to making games that are accessible to players of varying time availability and levels of commitment. Conferences and newsletters on casual gaming and casual gamers are springing up like mushrooms, so clearly it's on the agenda. But I think not enough game designers have internalized these ideas; not yet.
Edited to add: Even if you're not in the habit of reading comments here, it's really worthwhile to take a look at the comment left by Greg Gibson, one of the developers of Majestic. It is nothing short of a critical and thoughtful post-mortem of Majestic, from an insider's point of view. Great stuff. :)