I think W realizes that publicly declaring "we are going to nuke the bastards into the Stone Age" doesn't make for a good speech.
Lol. Even if he used his best John Wayne imitation?
"The transfer of nuclear weapons or material by North Korea to states or non-state entities would be considered a grave threat to the United States and we would hold North Korea fully accountable to the consequences of such action."
When you say grave threat, and you will be fully accountable, that is pretty serious in diplo-speak. A grave threat is answered with grave measures, not sanctions.