The default administrator login page (when one is not currently logged in) contains only one textfield -- administrator password. And almost for sure user will want to enter the password there. So Web UI can provide some help to the user by focusing the textfield, so user will not need to do extra mouse click or to move focus with keyboard. This makes administrator logins faster and smoother.
The attached patch was tested against Firefox 1.x/2.x, Opera and IE 7.
I had made the patch only for the English template. If you're happy with it, I can make a patch against all template pages.