Well, I guess there is a partial "mea culpa" is in order here.

As I was looking at the dll files included in my Visual Studio deployment project, I noticed that the QtCore4.dll and QtGui4.dll files were being pulled from my Miktex installation on my machine, not the Qt directory. A Visual Studio deployment project automatically includes dependencies that the application requires - in this case QtCore4.dll and QtGui4.dll. But since the MikTex was higher up in the PATH hierarchy on my computer, it pulled these files form MikTex instead of my Qt installation.

So, a warning to everyone setting up a deployment project: Make sure the Qt-related dll files being deployed are the right ones!

I say partial mea-culpa because my initial complaint still stands: Qt documentation does not include adequate information about deploying the assistant; it fails to mention the need for the sqldrivers directory with the Qtsqlite4.dll (or whatever it's called), and the need for both the .qhc and the .qch file. I must say that the reason I'm disappointed is that I have found Qt documentation to be quite good in almost every other aspect of Qt that I worked with, so I find the inadequacy in this area to be surprising and thus disappointing.