The damage with nukes is indeed greater, and the assured destruction of all of the North Korean govt. along with it would be the result. China likely would not tolerate a nuke detonation in it's backyard. It would reflect badly on them if they didn't support us when they need U.S. support so badly, especially with Taiwan causing issues, and their newfound trading power with the U.S. just on the upswing. You also have to remember Tiannemen. Many high ranking officers, and their troops refused to cooperate with just suppressing students. It's unlikely they will give their lives for the North Koreans after North Korea nukes U.S. troops. They might if we are the aggressors without reason though.
My take on this:
We have to play this particular game according to the rules of the orient or lose the advantage. Everyone knows the U.S. is the dominant military and economic power in the world. It's not necessary to remind them. If we polarize the Chinese and Russians through our aggression, it's not going to help us. We should play until they (North Korea) commit to an action, any action. At that point, they are locked in and will have to follow through on their promises, and our response would be nothing more than the penalty or reward to their actions. Reality discipline at it's finest.
This stands in contrast to Iraq, where Russia, Germany and France only cared about the money and public image, and disliked Iraq already. The penalties for our actions were limited to bad feelings, and words without actions.