The issue is that stories older than 2 weeks will never be unread, period. Stories are automatically marked as read at the 2 week limit. At that point, if stories were left unread, you’d have a heck of a maintenance job to do.
I would love to disable the mark as unread button for stories older than 2 weeks, and I have it on my list, since it’s not terribly difficult to do. But the real issue is that you would like to keep a bunch of stories unread for as long as possible. Perhaps saving those stories would help? Why do they need to be unread? Couldn’t you read them in their read state, since they are all more than 2 weeks old?
Ideally, I’d *love* to get unreading working for stories older than 2 weeks, but it’s an enormous amount of work—time that I am spending working on the iPhone app, the big social features, and a ton of other bug fixes. I prioritize unreads beyond 2 weeks as a lower priority improvement since it’s such an edge case.