The problem is not that the serial mouse does not work, but that it need to be configured to work.
And when installing Ubuntu we do not get a chance to configure it, unlike what some other distributions (Mandriva, PCLinuxOS etc) do: if they do not detect a PS2 or USB mouse, they go into mouse configuration, asking for port and interrupt, and then on to a mouse-testing page where you can move cursor, click right and left, before going back to the mouse config or exit once you have it working.
The problem is not that the serial mouse does not work, but that it need to be configured to work.
And when installing Ubuntu we do not get a chance to configure it, unlike what some other distributions (Mandriva, PCLinuxOS etc) do: if they do not detect a PS2 or USB mouse, they go into mouse configuration, asking for port and interrupt, and then on to a mouse-testing page where you can move cursor, click right and left, before going back to the mouse config or exit once you have it working.