Well, I did the dance with PowWeb support, gave them a temporary admin account and was told the following on 06/23/2010:
I did login and I see the error that you are talking about "unable to fetch update" although it shows that the core of the application is updated the modules and the applications where the problem occurs. As I refreshed it would show different applications or modules that they are up to date. For this problem you will have to research it with Drupal to find out what is causing these repositories unreachable to check for the updates. The application itself is working fine on the server without any restrictions the problem/bug is with the updater. I highly suggest researching this problem on Drupal forums and see how other users corrected this issue.
If you have further questions or concerns please let me know.
Basically, he is saying the problem is with Drupal's update service and not with PowWeb. He totally ignored the fact that these update checks work perfectly from my test server in my office. I have not yet reopened the ticket as I needed to get on with my life and get other work done. When I have more "free time" to look at this I will reopen my ticket with PowWeb.