"And ATSC 1.0 color gamut is actually a hair smaller than
that of the NTSC it replaced. "

You lost me there, what do you mean by that ? The different broadcasting format should have nothing to do with the colors that can be displayed, that is a function of the panel, or CRT. (actually a plasma panel is like a CRT in a way but it just has multiple rays)

Now LCD panels might be limited by the backlight. They cannot display any color that is not in the spectrum of the backlight. Actually they could not handle the colorimetry required for LED backlighting until recently when the new generation of LEDs cam out that actually have a phosphor.

Older LEDs had very spikey outputs. If a color isn't there you must display two colors opposite the wavelength you want in the right proportion so the eye mixes it. It was just too much to deal with so they went with the CCFLs.