Well, strategically speaking, there might be a time when severing a potential access to sensitive areas might be necessary. If a Kill Switch could be created, which would ensure a nations exclusion for the WWW to protect itself from cyber warfare and cyber invasion, it'd be a strategically important defence.
Hell, if a nation only excludes itself from the Internet instead of ruining it for everyone, I don't have much against it. Besides, it'd take -a lot- to convince any commander to sacrifice the potential of the Internet. Not to mention pressure form civilian enterprises (and corporations which have a ball busting grip on the US government).
I guess the biggest issue would be how to re-integrate a nation back to the WWW once it's severed.
Still, I'd consider it odd if there wasn't even a discussion on the validity or use of this type of, admittedly extreme, defensive measures.