CBS and Rather know it wasn't Rove. That's why they are standing by it. They know where this originated, and they know it wasn't from Republicans. If they believed the right was giving them false information, that would have been the story.
Not unlike that Joe Wilson/Valerie Plame "leak".
The media would upchuck that Republican's name so fast our heads would spin.
That's why they are keeping their mouths shut and risk being held in contempt. They know it was one of their Comrades.