NaySayer: confirmed again. I had moved — not deleted — these sub-folders from Programs in ProgramData: Accessibility, Accessories, Administrative Tools, System Tools, Tablet PC.
I assume the update routine modified (overwrote) a system exe or dll and then 'refreshed' the corresponding shortcut in one or more of these sub-folders. Perhaps it checked for the sub-folders first … whereupon the null return terminated the update.
For the future, I have made a backup copy of these sub-folders (with their shortcut contents) so that they can be reinserted when a Windows update requires them.
This is another instance of Microsoft curtailing user-customization in Windows 8; the price on the Desktop side for the folly of the integrated Metro side, IMO.
P.S. Thank you for the doing the original leg work of this troubleshooting!