I've heard that before and it just sounds so strange - why would interpolated frames on a HDTV remind people of the production values from standard definition televisions?

It's the frame rate. People are accustomed to seeing video at ~30fps. But old soap operas were somehow at ~60fps, among other things. I think this motion interpolation thing looks significantly worse than the old soap operas, because the interpolated frames break down when there's too much movement, which is exactly when they could have the most value, if you believed they had any value proposition at all.

I've seen those soap operas and it's true. I'm having trouble finding an online source that really shows what it looked like.

The number of people who've never had to watch an old soap opera is increasing.

I still don't understand what that means. I've never sat down to watch a soap opera, so I have no idea what they look like.