Both the actors and the models (ships etc.) were shot on film. Those filmstrips that came out of the camera were then transfered onto video. Post production was then done on video. But let's not forget shots with actors on the set (except those with transporter effects and phaserbeams) are just that, one shot. A shot of a ship is actually the mix of several different layers (a black matt + a shot of the exterior of the ship + a shot of the inside lights of the ship + a shot of the naccelles lights + a starfield + a planet etc.) Today the mixing of those shots can be done digitally inside a computer (that is if they don't opt for CGI alltogether). Back in the 80's they had to do that with analogue video tape recorders. So immagine using 3 video recorders, let's call them deck A; deck B and deck C. You put the videocapture of the starfield in deck A and the video capture of the planet in deck B. Mix those shots with a mixing console and record the mix with deck C. Then you take the tape out of deckt C and put it into deck A. In deck B you put the video capture of the black matt. Again you mix and record the mix onto a new tape in deck C. Then you take that new tape out of deck C and put it into deck A. In deck B you put the videocapture of the exterior of the ship. Again you mix and record the mix on a new tape in deck C....
Now remember that analogue tapes added noise to the recording. So by the time your shot is complete it will be quite a bit noisy and it will have lost a lot of it's sharpness. That's why those shots were so different from the shots with actors.
I think the reason is a vicious circle. Why would TV networks invest in HD equipement when most people don't have a HD TV set. And why would the people buy HD sets when none of the networks have HD broadcasts. So if the government doesn't do anything about it, no one will.
BTW: Come and live in Europe for a time. Here the governments involve themselfs with just about anything. Perhaps the reason why the US government became involved is that if they don't Europe will win the HD race.