They're creating the assumption that Chinese Gov't or independent parties are hacking systems for gain. The statements of "they leave no trace" or the like attribute to the fact that there isn't any evidence through google or otherwise.

As far as I'm concerned there is evidence of some high profile hacking teams somewhere in the world doing some nasty stuff (such as the fraudulent certificates and hacks on companies that was tied back to Stuxnet). We don't know for sure who does it but a lot of people assume the chinese based off of (what I think) is IP traces.

Its all speculation. We know that someone is hacking, just not who. Its obvious that they're good because there hasn't been enough evidence to pin it on anyone. As anyone on this site should know: IP isn't a very good identifier and even less so for professionals.