The Chinese have their own versions of almost every main Internet site outside of the country.
Instead of Google, they have Baidu.
Instead of Google or Yahoo news, they have Sina.com.
They also have their own social networking sites like xiaonei.com.
Want to sell something on a site like eBay? Go to taobao.com.
Foreign firms have a hard time penetrating the Chinese market. And when they finally get their paperwork approved, like Facebook did recently, do they find out they got in too late and now they're stuck with using their name more as a marketing tool than having registered users.
And another reason is that these copy cat sites are launched and established so quickly so that foreign-owned sites don't even get a chance to get in first so that they can build up their users. That way when sites like youtube.com.cn finally get in, it's not a novelty anymore.
But another possible explanation is that it's a way for the Chinese government to keep its people living in a cyber bubble. As long as there are google-like sites like baidu and social networking ones like xiaonei that are in Chinese, the public will think it's fantastic and use them.
It prevents the people from looking elsewhere to consume news or place their lip-synched videos on sites outside of China, where they could possibly get new ideas...