I wasn't disagreeing with you
Although I focused on microphone and recording technology as a factor, I did acknowledge patterns of speech changing too.
Let's explore this a bit more scientifically--we have recordings of men doing the news going back almost a century. Picking a genre controls for content as a factor in speech patterns.
Edit: Ah hell, embedded YouTube videos have stopped working because of https encryption. You'll have to click the URLs instead of using the player (I left them embedded in case it's just me or my browser or my computer or my karma or something.)
[youtube]
USS Macon crash 1935
Hindenburg newsreel, 1937
[youtube]CgWHbpMVQ1U[/youtube]
Edward R. Murrow, 1954:
[youtube]vEvEmkMNYHY[/youtube]
Walter Cronkite, 1968:
[youtube]Nn4w-ud-TyE[/youtube]
Brian Williams, 2011
[youtube]WnxC7yiezN8[/youtube]
I hear a steady evolution (or maybe "devolution" is the word) toward decreased formality, along with relaxation of grammar rules.
Another set of samples comes to mind if you want to study the evolution of British (recorded) speech: Dr. Who episodes from 1963 to the present. Or, back on this continent, the "Weekend Update" segments from Saturday Night Live, from 1974 to the present.