What Explains the Decline in Reporting on Social Unrest in China?

In 2004, media reports on incidents of domestic social unrest in China were frequent and widespread.  Beginning in early 2005, official Chinese sources began to report significant declines in the numbers of both mass incidents and citizen petitions.  At the same time, media reports regarding incidents of social unrest tapered off.

Official Chinese sources attribute these developments to official success in resolving citizen grievances.  But there is another possible explanation: official directives issued during this period that ban media coverage of mass incidents.