I agree with you in part, but what makes you feel that China could not respond? Just curious. I thought they had a pretty beefy nuclear arsenal themselves.
Time factor, sub launched missiles would take out the command stucture in a matter of minutes. Peking would be glowing before they could be alerted.
Surviving military would not know who hit them (could of been the Russians for all they know) and with the EMP pluse distroying communications plus the fallout and destruction they are going to be busy with their own problems.
In a communist country like China who has been conditioned to take orders from above if you take out the leadership the followers is most likely to surrender than fight.