China has implemented the Great Firewall of China, both to monitor and control their citizens, as well as to limit the ingress points into China (three major ones if my memory is right) so they can more easily monitor and cut the lines if attacked. Compare that to the United States which has so many major lines running into/out of the country that it would be nearly impossible to block an attack from outside (not that inside versus outside is truly a big difference). Since these attacks are coming from behind the firewall, and little or nothing is being done to stop them, it is easy to conclude that the government is choosing to allow them to happen. Compare this to the news stories of Chinese citizens being arrested, tried and executed for hacking internal Chinese companies.
Now consider the philosophy difference between the Chinese and Americans, where the Chinese people are raised to believe they have a duty to perform actions to help their country. The government doesn't have to tell people to hack into systems in other countries to collect useful information (which they also do), they just have to make it known that the information is desirable, then not block the attempts by the "non-government" hackers (see my first paragraph). If a citizen later has come into possession of valuable information which they choose to share with the government, then they are just being a good citizen. We call it hacking, China calls it patriotism.
So why does China now respond? Because they are walking a tightrope. They are seeing how far they can push things before it has an unacceptable consequence. That is also why I think we chose to speak up this time, because to always remain silent just lets China continue doing their antics with no real consequences. So why this time and not others? Because if you keep telling the attacker what you saw, and by implication what you didn't, you give him valuable information that can make him more effective and more stealthy.
It may not be the classic form or war, but it follows a lot of the same rules. And because of the difference of philosophies, it is a somewhat asymmetric war.