something to ponder?

I heard on a radio news item this morning Obama is going to (as a nuclear weapons reduction measure) promise to not use nuclear weapons against any enemy that does not itself have such a capability even should they use biological or gas in their attack but would use instead to devastating effect conventional weapons?
Now the US is not stupid, I can�t help but wonder just what advanced weapons systems they have developed or developing in the conventional sense that gives them assurances that they can say this?
Now I don�t claim MST systems are included here ............but it does just make one wonder?
Cheers,
Mrdog.