Well without the documents how in the hell does Rather know the story is true??
It has long been received wisdom among liberals that Bush skipped out on his guard commitments and used his family's influence to get special favors. Liberals believe this as devoutly as any conservative Christian believes in the truth of the tenets of his faith.
Because the allegations are obviously "true" to Rather,in his mind documents MUST exist that evidence their truth. But suppose some evil Bush lover destroyed the documents? In that case, there is no harm in recreating some memos that capture the essence of what the missing documents must have said.
Thus, Rather says slyly, "The story is true, there will be no retraction." And McAuliffe says, "The seriousness of the charges is more important than the documents that reference them."