Everyone has rights to free speech, and you can tweet whatever you want on Twitter social networking site. As Twitter expands its reach to other countries, it seems like the company may be introducing censorship due to content restriction in some countries.
According to their blog, Twitter has always supported freedom of speech. But with the expansion to other countries, there are restriction of content from specific countries. The company is refining its technology such that even if messages are censored in that particular country, the content could still be seen by the rest of the world. This is certainly a far cry compared to erasing a tweet that will disappear from the world. In addition, Twitter will also post a censorship notice to alert user when a tweet is removed. This is somewhat similar to Google's way of removing a search result when required by law, by the country.
Source: Associated Press