On Google's official blog, they explained the decision:
Google users in China today struggle with a service that, to be blunt, isn't very good. Google.com appears to be down around 10% of the time. Even when users can reach it, the website is slow, and sometimes produces results that when clicked on, stall out the user's browser.Wikipedia, in contrast, refused to censor themselves. The Guardian reported:
This problem could only be resolved by creating a local presence, and this week we did so, by launching Google.cn, our website for the People's Republic of China. In order to do so, we have agreed to remove certain sensitive information from our search results. We know that many people are upset about this decision, and frankly, we understand their point of view.
Filtering our search results clearly compromises our mission. Failing to offer Google search at all to a fifth of the world's population, however, does so far more severely.
[Wikipedia co-founder Jimmy] Wales said censorship was "antithetical to the philosophy of Wikipedia. We occupy a position in the culture that I wish Google would take up, which is that we stand for the freedom for information, and for us to compromise I think would send very much the wrong signal: that there's no one left on the planet who's willing to say 'You know what? We're not going to give up.'"It is starting to seem that even granting Google its excuses, Wikipedia's choice has been wiser. The Chinese government has been blocking Wikipedia for a year, but they have just unblocked it, likely because there is so much public demand. Boingboing.net's Cory Doctorow writes:
China needs Wikipedia and Chinese net-users would access it using circumvention tools -- the block on Wikipedia made Chinese Wikipedia users into automatic dissidents.
Beijing is now stuck playing cat-and-mouse with Wikipedia, having to ferret out every potentially sensitive page and update its filters accordingly. If MSFT, Yahoo and Google followed Wikipedia's lead, we could force Beijing to devote ever-escalating resources to this effort, a denial-of-service attack on its censors.