No, FR is not blocked or flitered in China (just ask any of the many Freepers who has posted from China while traveling or are currently living / working here). Don’t think it ever has been blocked or flitered in my experience.
Mainland Chinese has pretty much unfettered access to major western media / political / news forums (one interesting aspect of Chinese censorship - it’s more focused on monitoring access to Chinese internal sites as well as some overseas Chinese language sites, but not external non-Chinese sites).
Most English literate Chinese people (and that’s growing by a lot these days, including pretty much anyone who is college educated, and ever more so since English classes are now mandatory from 5th grade onward) are keenly aware and interested in how the West sees China and how news about China are reported and discussed in the West.
For sure a lot of my collegues in Shanghai are spending their spare time at work surfing the net and checking out international news coverage.
So, to answer your question, they are here to see and hear how the world is reacting. And no, they’re not just on FR (maybe it seems that way to you if you only hang out here), they are on pretty much all the major English language news forums (check out the comments on news stories relating to Chinese quake on all the alphabet network news internet sites, BBC, NYTimes ... blah, blah, etc, heck, they are all over YouTube too).
That’s not entirely true. China-based FReepers had trouble accessing the Net after their PsyOps expert/FReeper troll “pganini” was exposed as a ChiCom agent and was banned a while ago. AS somebody who is in constant touch with freedom lovers in China, I know this for a fact and other FReepers can attest to it.
Additionally, we have a US-based FReeper whose blog has been banned by the ChiComs and continues to be banned.
While I see no reason to doubt your experiences, these are subjective and are not representative of all FReepers who post in China/on the bloodthirsty ChiCom regime.