There was an error in the dependency specifications which somehow triggered a major failure in AppStore.app. Most of those problems are now fixed, but while wrestling with it, I discovered /var/log/install.log
Every time I go to the Updates panel in AppStore, that log shows a detailed record of the scan for updates. This record always ends with a list of seventeen available updates: 16 Voices and a Gatekeeper configuration. Yet AppStore still says no updates available.
How can I get those items to update? For the voices, I could probably deselect them and re-add in Preferences, but that seems pretty silly and doesn't help Gatekeeper. Update: Don't have to deselect voices. Selecting customize from the voice menu in Speech prefs shows the ones selected, and just clicking OK starts the update. I'm going to file a bug report that Software Update won't do it. And I still don't know about Gatekeeper. That's probably some other obscure location in the preferences.
By the way, part of the AppStore fix was a reinstall of the OS without a disk wipe. So why did not these items get updated during the reinstall (by internet with Recovery partition)?