So, Dan Rather steps down, but not out. According to Drudge, this was announced now to separate it from the investigation report, whatever that might be.
I'm pretty sure that Rather knows what the report says, and I'm pretty sure it's been handed in. The report is scathing. I believe CBS' brass is sitting on it until they can either get it toned down, or at least can get their spin going.
So, in hopes that he can cut his losses, Rather steps down ahead of the bombshell. It won't work. This whole thing has been too little, too late, and this is more of the same. Look for Sumner Redstone to react badly to the report when issued and drop the other boot.