The previous behavior was to acknowledge the leaks and try to contain them. The current behavior is to arrest people who document the government cover up. Why the change in behavior, unless the government absolutely knows what happened and is trying to control the information?
Your China article is from 2004. China's regime's ability to control media and its residents is stronger now than then, and the people in charge are more insecure and defensive. That may be enough to explain the change in PR strategy.
Alternatively, past leaks simply weren't bad enough to embarrass the State and could be blamed on local officials. This one got so big so fast that a more defensive posture was required.
The previous behavior was to acknowledge the leaks and try to contain them. The current behavior is to arrest people who document the government cover up. Why the change in behavior, unless the government absolutely knows what happened and is trying to control the information?