The story moves on. Whether Dan Rather likes it or not, this story is going to move on. If they wait and convene a panel and declare the documents inauthentic in a few days, it won't make any difference because that will be old news by then.
There are a lot of interesting parallels between this CBS memo story and the Swift Boat Veterans for Truth story. In both cases the mainstream media felt like they were in control of the clock. They delayed acknowledging known events, with the effect of exacerbating rather than ameliorating the negative impact of stories which played against their candidate.
Both the Democrats and the left-leaning media would do well to realize they cannot control the dissemination of information (anymore), and it is in their own interest to not pretend to do so. They could take an object lesson from their nemesis Mr. Rove. As soon as he got the memos, he released them without comment. The White House simply said "we don't know if they're forged or not", and stayed on message. The truth doesn't have to hurt if you don't let it.
In military parlance it's called the decison cycle, and thanks to AlGore's Internet, we are most definitely operating "inside" the MSM's timescale. Their relatively few reporters, additonally burdened with bias in a lot of cases, cannot out-investigate thousands of netizens with a wide background of expertise.