"Just as the magnetic pickup liberated the guitar in the 50's and allowed it into the 'big band' era, maybe to partly answer Richards original question, the microphone has 'liberated' the human voice. Singers both male and female are now able to use areas within their vocal range that would not have been practical just using the unamplified voice. As 'folk' music acclimatises itself to the 21st century, singers are experimenting with the new technology available to them."

Two words: Bing Crosby

I disagree that vocal range can't be done unamplified in a good acoustic environment.
I think that many singers depend too much on mics. Live singing without amplification is
preferable (in my opinion) for folk singing. It's more intimate.

A good singer doesn't limit him/herself to head voice, chest voice etc. but has a range of expression that encompasses many timbres. They do this and keep their voice over the years.

Belting is dangerous for the vocal cords. I know of one prominent performer who has lost the ability to project in singing through faulty technique. I won't mention his name although many may know who this is.

Sometimes performance which is based on image, personality, acting, etc. can appear more exciting regardless of vocal technique but in the long run, the voice doesn't last.

Here's another factor. The more one learns about good vocal technique, the more one wants to hear people practice it.

Frank