internet - Alltheweb.com blocked?

Is the search engine alltheweb.com blocked or not? Isaac Mao reported it first and since I never used this website, I checked it and got right away access.
This evening I saw his entry again, checked it from Shanghai and I was really a classical block: I could not get to it without a proxy. Very strange. I'm not familiar with the service, but they seem to use the google-technology when I look at the result of searches. Why would somebody block them and not Google? Censorship and logic do not go together.