I think they have finished their business in Tibet. That's why no need for the ban anymore. Also it spoilt their image to be censoring you tube, so I guess once they finished they just let you tube continue.
That is possible. or may be youtube have contacted Chinese government and asked China to allow youtube,maybe there is a agreement between them.
Google has been known to obey some instances of Chinese censorship so this is possible. Maybe check you tube to see if the Tibetans protest videos had been removed?
Hope my site will not be blocked,I noticed that some porn sites also blocked,and blogspot.com blocked by China too.I guess google need another big deal with Chinese government so that people can visit blogspot.com from China.