This is quite smart, as it is highlighting that China itself allows Chinese in Hong Kong much greater freedoms than on the mainland. If they block google.cn (which is likely) they are saying that Hong Kong Google is breaking Chinese law.
Searches from China must pass through the Chinese government’s extensive web filters – collectively known as the Great Firewall – which automatically weeds out anything considered pornographic or politically sensitive.
The move, in effect, shifts the responsibility for censoring from Google to the communist government.
And this is how it should be. Personally I want no censorship at all, but if it has to occur it should be the Government, not the search engine provider, that does it.
UPDATE: The SMH also reports Google has done a submission to the Australian Government strongly criticising their Internet filter, and warning it “would enable future governments to use it for political censorship”.