According to WSJ.com’s article, in term of censorship Iran can do more by doing deep packet inspection compare to China.
But it is understandable as Iran’s Internet user is 23 million, compare to China’s 300 million strong. Because of China’s geography, China’s monitoring infrastructure is decentralized, compare to Iran’s centralized policy. Because of this policy, when Iran activated deep packet inspection to monitor traffics, users felt an access slow down especially after the June 2009 election.