Because the default server in Hong Kong is very very slow.
From menu bar:
System > Administration > Software Source
In the 1st tab of Software Sources,
There is a box of 'Download from'
use the mouse to select the down arrow, and then select 'other',
Ubuntu will then prompt you to select the best server available to you.
In my case, it is now set to
http://ftp.hostrino.com/pub/ubuntu/archive |