Apple Mobile Device Ethernet - iPhone Tether - via USB was not working. Then...

I searched high and low on the internet. Should have just come here to start. My particular answer was some combination of

1. Update iTunes - which installs some additional folders in "C:\program files\common files\apple\mobile device support", one folder of which is "Drivers"
2. Inside the Drivers folder is a setup information file, usbaapl64.inf, which windows can install directly with a right-click and select "Install"
3. Done. The "iPhone Tether" connection in Network & Internet Settings | Change Adapter Options no longer says "Ethernet cable unplugged". Now it shows the device, and I'm cruising on USB tether with wifi shut off!

happy dance now... :)