Then they'd have to produce the originals.
Your theory only works if CBS had told us, up front, that the originals were handwritten.
Pulling that out of the hat now looks like a shell game, and CBS would look even slimier than it does now.
Only to people who think rationally, and that's not the intended audience. What they are doing (possibly) is creating a circumstance under which it will no longer be viable to question the authenticity of the handwritten docs, as perceived by irrational emotionally-driven idiots who get their news from Dan Rather and his ilk.
I hope I'm wrong about this, but I wouldn't put it past them to try it.