I've tried it now, and there are no problems downloading during the installation.
During the online part of the installation, two different servers are used, to minimize the risk of not being able to download if one of them might eventually be offline. They are selected randomly at each installation so, if one of the server was down (we don't have any report of this, but it might happen, maybe for a brief time), you might just try it again, hopefully the installer will pick up the other server on the next run.
If this doesn't fix it, the problem is then surely something in your system which is blocking online access to from the installer to the download servers, like an antivirus, an anti-spyware, a firewall.
But keep in mind that, the whole point of the Stand-Alone Addon Manager installer, is that you download that one, to get all the latest updates. Which means, if you just downloaded it now, you can be sure the files contained in the installer ARE the most current version, so you don't NEED the online files, because they are exactly the same version.
The installer can obviously work offline, it's enough that, when you see the "No Internet Connection, press Next to use local files" message, you do what the message says, and press the Next button, so the installation will continue using only files contained in the installer which, if you just downloaded it, are the latest version.
