Thanks to all who read my post. I resolved my problem with the eight Flash Player-related 'Medium' registry errors that showed up in jv16 PT 2008 after I manually removed some old Flash Player entries from the Windows System 32 folder due to the Secunia Personal Inspector telling me that these outdated Players were insecure.
I did it using Adobe's latest (April 08) Flash Uninstaller in Windows' Safe Mode. This uninstalled my current Flash 9 Player. Then I rebooted into Safe Mode and used jv16 PT 2008 to clean the registry. In Safe Mode, it was able to delete what it previously could not delete, the aforementioned undeletable eight Medium registry errors, all related to Flash Players.
As a final step, I reinstalled the latest Adobe Flash Player 9 in Safe Mode as well. I rebooted to the normal Windows mode, then ran the jv16 PT 2008 reg cleaner again. The eight undeletable registry entries were gone. I was happy to see these results, as I try to keep my registry in good shape.
So the final answer is that these were NOT false positives on the part of jv16 PT 2008, but WERE unfixable in Windows regular mode by either jv16, or by using Windows Regedit manually. It must be that Adobe works with the Windows software to make these registry keys off limits even to an operator who has administrator rights, but I am guessing here, not being a programmer, or Windows expert.
For the sake of information completeness, I run jv16 PT 2008 in its 'aggressive' registry cleaning mode, which is one notch less thorough than its most aggressive cleaning mode. My jv16 PT 2008 version is currently version 1.8.0.459.