That makes sense, as broadcasting became less of a novelty, the tone tended to become more conversational. Something similar would probably happen in films, as people became familiar with the new medium, and old stage actors were gradually replaced by coached film professionals.

But that still doesn't explain the rhythm and cadence of the speech, the phrasing and timing. Think "Forties Bomber Crew" dialog. Sure, its stylized military technical talk, and an attempt is made to showcase an ethnic, class and regionally diverse collection of accents, and it is peppered with swell period slang. But overlaid on that is a quick, snappy, wisecracking delivery that may or may not reflect the way real people spoke at the time. Its something that must be
listened for, it would not be noticeable if you were just reading the script.

I wonder if our parents spoke that way. I don't remember. My mother had a Bronx Jewish accent til the day she died, and my father supposedly had a Spanish accent, but accent is not what we're talking about here. I have read some of their wartime letters and other writings, and I am amazed how articulate and eloquent prose writers they were, considering they were only high school graduates--a secretary and a sheet metal worker.

They wrote in English, to not draw the attention of wartime censors.