I’d say that your friend doesn’t know what he’s talking about when he blames the speech clarity on being due to analog vs digital. What your friend may not realize is that when you watch old TV shows and movies, they’re actually digital copies of the analog films, not just for the picture but also for the audio as well. So for sure as hell it’s not an issue between analog vs digital. It’s an issue between mixing style instead. New movies and TV shows tend to put the voice through a lot of processing as part of the mood creation, quite often way too much sound processing unnecessarily if you ask me. Usually less is more, and that’s exactly the case here. Older movies and TV shows simply record the voice and play back as is, without adding much of any processing through it. The result is unadulterated clarity on the speech. I know exactly what you mean because I’ve watch my share of modern TV shows and movies where I could not believe what they did to the voice and not realize how badly they’ve botched it up.
Similar situation with music oldies version new music. I guarantee you if you record your LP into mp3 format and play it back on your iPod, you can still get the same clarity on the lyrics, unchanged. There are some people who call themselves audiophiles and prefer to listen to old vinyl albums instead of their digitized mp3 version. I really wonder if they’re subjected to a blind test whether they can really tell the difference between the analog playback and the digital playback of the exact same oldie content. I suspect that it’s the same case here where old LP music were recorded with much less instruments and soundtracks, so the simplicity of the recording is what enables better clarity on the lyrics. Meanwhile modern music producers have all the means to add in any kind of instruments and/or sound effect very easily at the tip of their fingers, causing the lyrics to become muddy in the process. Again, I think it’s the case where less is more here.