[dtvmcdonald]

"as UHF was used in the US, and in most other countries to provide additional, local services, with VHF (with its vastly superior propagation characteristics) continuing to be used for nationwide services"

That's simply not true in the US. Many cities right from the start had no VHF station,
and almost all had insufficient VHF for the usual original three networks plus one
local. When PBS ("public") became the 4th network it got worse. Most of the US has never had much use for "gap filler" transmitters, except Utah. Only the maybe the 10
biggest ... and islolated ... cities had an excess of VHF channels (e.g. New York
and Los Angeles, and even New York had one officially across the river.) The east coast
has cities too close for VHF.

Also note that we had coverage of even modest size cities with one or two stations
long before coaxial cable and microwave networks. They had to do network
programs on 16 mm film.

Note that in the US external UHF preamps were readily available and worked
well enough.