Well, I figured out what the problem was -- My blind faith in Fantastico.

Instead of doing "the right thing," I said, "Sure, Fantastico, go ahead and update my Drupal installation."

Fantastico, with all the finesse of an immune system on overdrive, blew away my subdomains -- "This ain't part of no Drupal installation" -- and "poof!" they were no more.

That'll learn me, durn me.