"Before I wrote my first cognitive book, I got a bit of advice from an editor, which was probably the best advice I ever received. She said that the problem many scientists and academics have when they write for a broad audience is that they condescend; they assume that their target audience isn't too bright, consists of truck drivers, chicken pluckers and grannies knitting dollies, and so they write in motherese, they talk down. She said: "You should assume your readers are as smart as you are, as curious as you are, but they don't know what you know and you're there to tell them what they don't know." I'm willing to make a reader do some work as long as I do the work of giving them all the material they need to make sense of an idea."That would also seem to be true of television.
The very best documentaries assume the viewer has an intelligence and happens to be interested in the given topic: Michael Wood, Mary Beard, David Attenborough and Brian Cox and the best stuff on BBC Four all fits into this category.
Judging by Civilisation and The Ascent of Man that was the tendency in the past too.
The worst assume the audience is bloody stupid, needs everything explained to them and barely manages to scrape the surface of the given topic (most of Channel 4 these days and the worst stuff on BBC Four).
I can still remember when I first began listening to Radio 4 and couldn't believe how much respect it had in my ability to listen and understand what was being said.