It is usually a copyright issue, or on some sites (not youtube, obviously), it may be conservation of bandwidth. BBC programmes are not available on iplayer outside the UK, is this censorship by the British government?
The BBC do this for "entertainment" content, as do others, but not for news content. Outside of the UK, there is a separate BBC channel containing factual content such as world news, and this IS available from the iPlayer outside of the UK.
The problem with the internet is that many sites link to US news channels as reference material, rather than sites from other countries. This is really down to the "America owns the internet" concept, but it leads to people outside the US running into these "your country is blocked" issues.
I very much doubt Chinese citizens have licensed access to this content, yet far from blocking it for "copyright reasons", the same US broadcasters are complaining, via the government, that the Chinese citizens are having their human rights violated by being blocked from accessing the same content that UK citizens are being blocked from seeing.
An actual example I remember recently was the recent tornado devastation in the states. I found more about it via Google, but then ran into the "your country is blocked" problems on some of the coverage on websites. The coverage was clearly intended to appear on these free to access news sites, so the block was not down to a "pay wall" on the site. This means that I am able to look at the UK media coverage on the story, but not the coverage from the US sites, and unlike the BBC news teams, the US reporters were actually there, and were able to give a better account. Only later on did the BBC content catch up, and later still we have a couple of science documentaries about the event.
This illustrates my earlier point that the US censors the internet just as much as China. The difference is that China does it in order to preserve it's system of totalitarian control, which is threatened by information from outside reaching citizens in the raw state, rather than the modified state from the state. In America, the "information is money" concept drives a policy of blocking the unfettered free access to information, even blocking content that CANNOT be turned into money such as breaking news stories.
Have you EVER seen the 6 o'clock news out on DVD?
A news bulletin is virtually worthless the next day, it's only purpose then is to form part of a history archive for future generations.