Answers: Because China is trying to keep it's ancestors from learning almost its past, e.g. the Tiananmen Square massacre. Its purely generally a appropriate way to maintain people from finding stuff the establishment doesn't want them to know, since wikipedia is so widely used and has so much info
Its adjectives due to the PRC governments censorship law. The site was second blocked in August this year (2007) and at hand has be no indication of it being unblocked again.
There are ways to circumvent the block, any by using proxies which will allow the users to view but not gag wikipedia articles, or by a company called psiphon software, which aims to serve users circumvent the block (
http://psiphon.civisec.org)