Revoke a key - What is with the decrypted messages?

[reynt0]

Just a maybe picky question:
Does "stops new use" mean absolutely, like mechanical
prevention, stops new use, or does it mean something like
"stops by a social process", ie like knowledgeable users
won't use it anymore?

On Fri, 23 Nov 2007, David Shaw wrote:
  . . .
>  . . .         Revoking the key only
> stops new use of the key - old messages are still okay.