The "Great Firewall" in China has over 600 million active Internet users. That's double the population of the United States. Baidu is the dominating search engine, there are replacement services for Twitter, Facebook, and others. Their IM "Wechat" has over 300 million active users alone.
In all reality, Google, Facebook, and others would _love_ to have even the smallest presence in China to get access to that user base. It's a gold mine just waiting to be cracked. Until they are, it will be referred to as "The Great Firewall", when in reality, Chinese internet users probably aren't really missing a lot, outside of politically charged sites, perhaps.
I don't think it's fair to say that Chinese users aren't missing a lot. At the end of the day, a small number of users are responsible for the overwhelming majority of quality content created and discovered (authorship and curation). Those users more often than not rely on high quality content irrespective of national origin. When you cut off that access for those people, it's certain to limit the quality, breadth and depth of what they create and share with their peers in China.
I expect this to be especially true with Twitter, which is often a very valuable back channel for many communities of interest (for example, a lot of prominent engineers in several programming language communities use Twitter as a way to share novel ideas and libraries).
When you cut off Chinese users from these sites, you cut them off from a lot more than just inconvenient political content.
China has more Internet users than most countries have for a population. It has a cornucopia of content and services that would rival the "free Internet" you and I enjoy. It's hardly a digital vacuum mainstream media would like you to believe. It's no North Korea.
Sure, there are social and political issues, but most Chinese Internet users are very happy with what's available to them. The reality is, there are two "Internets", and China's Internet is a very large one.
In all reality, Google, Facebook, and others would _love_ to have even the smallest presence in China to get access to that user base. It's a gold mine just waiting to be cracked. Until they are, it will be referred to as "The Great Firewall", when in reality, Chinese internet users probably aren't really missing a lot, outside of politically charged sites, perhaps.