Despite the varying reasons listed in the article (which I won't endorse those reasons), I think this might be more along the lines of general reality, IMO.
They are still good old boys, but the difference now is that N. Korea has not gone through 20 years of opening and China has. Some Chinese think of N. Korea as a friend, but a stubborn one unwilling to learn new things.
China wants N. Korea to open along the same route China has opened. In China's eyes, this is the ultimate goal.
China has "opened" but retains one party rule. They want N. Korea to do the same. Right now, N. Korea is somewhat of a burden to China in some ways. That 'burden' is not the most significant thing. Its more like 'North Koreans are old friends, just a bit unwilling to test new waters'.
China was doing its best to show N. Korea about the new Chinese style market economy etc etc. N. Korea did not bite just yet, albeit some Chinese think they were making headway. That is part of the reason why the Chinese are thinking Bush is going over the top and what they are critical of. Its the same kind of logic with the "sunshine policy".
The Chinese view in brief is that North Korea is a long term friend with a short term stubbborn idiot for a leader.
N. Korea today is about like China was 25 years ago.
China wants the N. Korean regime to stay intact. N. Korea is the closest thing China has to a best friend.
If N. Korea chooses to open, but remain intact, they will project a huge force in Asia. They will definately influence the South, and diminish "American" thinking in Asia.
I can see statecraft in all of this.
China has been working on N. Korea for a long time.