This is because we want good stories to have multiple chances at making the front page. The current story is a great example. In fact, we invited tdurden to repost it, as we sometimes do when we notice an article that we think the community might find interesting, but which fell through the cracks.
We're working on a better duplicate handling system that will reduce the number of reposts in the story stream, but getting it right is surprisingly subtle, and we'd rather take longer than get it wrong.
I wonder if it would be sufficient to show the author the other posts and ask if they still want to post it. Let them self select if they think someone else said it better or sooner.
