The New Government of China with Mr Xi as President and Chairman is a different government than that of Mr Hu and his social-engineering paradigm that has now departed.

Mr Xi is a much more savvy politician and his rise to leadership has unified the Chinese army in a way Mr Hu could never do.

China also pretty much has a brand new navy, brand new nuclear attack submarines - a lot of them -that still remain very difficult for the USA to locate at all due to an advanced naval 'sonar doppleganger' technology that the USA can't yet fathom China's main interests are stability on the Korean peninsula and protecting its own interests from attacks/incursions by the USA in strategic DPRK.

Mostly, China is interested in securing its sea lanes and Taiwan and the Daiyu islands, not in Korea, per se. China wants Asia to be free of American ongoing destabilisation.

Meanwhile Russia has a very big presence in the North of Asia and is ramping up its navy and airforce there to secure islands given to Japan, North of Korea, by the USA some years ago.

As for Korea, its territorial bordering and kinship neighbours are China and Russia and neither of these will tolerate any American presence in the north. 

America feels it is dealing with the same Chinese government it was dealing with last year, but Mr Xi, well, he is not like the past at all.