The list of repositories in the installer is much smaller than listed on the web site. Why?
In particular, there are no Australian repositories listed in the Installer but they are on the website.
Can I add repositories manually?
The update manager shows also a smaller list. As far as I can see it lists only the repositories which are intact and have no delay. If you really want to use one of the other you can try to start the installer (setupwiz) (and later the package manager mpm) from the command line and set the repository through the options: http://docs.miktex.org/2.9/manual/setupwiz.html. But I don't really see the point.