Technically, LW isn't about x-risk. It's about "refining the art of human rationality", as you can see up there in the header.
I am also not sure that a blogspot blog that gets 0-6 comments per post is really worth calling "a community" or taking particular notice of. The other ones you mention seem to more closely resemble communities, but have even less to do with x-risk.
Techically you are right. But my post was not about x-risks themselves but about tendecy of different groups of people aggregate around one partical x-risk and ignore other x-risks by for example not given them right to be called true x-risk.
"LW is a community of people who mostly share the idea that AI is the main existential risk."
In the survey results there is no agreement that AI is the most likely risk of killing 90%+ of the human population by 2100. There might plausibly be agreement that a bad outcome from AI is the most likely existential risk, on the theory that survivors can recover from the collapse of civilization from nukes or bioweapons eventually, though.
If it would be Venerian scenario with boiling water in oceans it would be x-risk. The mentioned blog claims that it is possible. I think that they a not right.
LW is a community of people who mostly share the idea that AI is the main existential risk. But it is not the only one community in the web which has large ammount of evidence about particular existential risk. And the main problem for my point of view is that both communities (but in fact there are many) do not aware about each other existence. This is a real bias.
Here I would like to present another group which I recently found in the net. I cant judge their arguments but find them interesting.
This is http://arctic-news.blogspot.ru/
Their main idea is that Arctic is melting very quickly which could lead to runaway global warming which could start as early as 2015. They explain a lot about positive feedbacks with methane hydrates, water wapors and provide many real time information, maps, satelite images to confirm their point of view.
My idea is not to start discuss arctic ice on LW or AI in Arctic news, but to point on existening of such separated communties which (because of confirantion bias) concentrated deeply of their own agenda. The other such communties are flutrackers, zerohedge, theoildrum and more.
And one probable property of confirmation bias is that a person not only overvalue his own pile of evidences but dismisses value of any other piles of evidences. And that is why such X-risks orientated communities exist in isolation from each other.