What you're saying is undoubtedly true, my grandfather was a professional orator who read aloud to industrial workers in noisy shops prior to the introduction of amplification, and he used certain techniques of projection and pronunciation (which he had honed as a stage actor) which he later had to adapt to broadcasting when he switched to radio in the 30s. He spoke often of the differences in technique required, even in Spanish. These included both projecting the sound to fill a hall, but also the dramatic emphasis and modulation used when reading fiction.

The effect I'm trying to describe here is different. I can hear a movie playing in another room and tell you within 20 years or so when it was made, even if the text being spoken contains no clues as to its time of origin. I can't quite put my finger on what it is, unambiguously, except to say "they are talking in an old style".

As for the differences between USA and UK audio, I've always found it so annoying I assumed it was differences in the technical properties of their audio engineering gear. Some of my Brit TV CDs sound so muffled and garbled I have to distort the tuning and balance of my audio equipment to understand the dialog. OTOH, their recorded music sounds excellent. I doubt they are really behind us in this area, and always assumed it was a transcription issue when copying their signal to our standards, sort of like the scan frequency on the two video signals being different. My copy of "Smiley's People" is so difficult to understand I have to run the audio through the tinny TV speakers with the treble boosted way up instead of my Bose Wave Radio. I can understand the dialog, but now the background music is distorted.