I said
"Part of the reason why the words in the 1977 version are so much clearer can be seen in the video: separate mikes for the voice and the guitar, and an appropriate balance between them (thanks, presumably, to someone on the sound desk). The later performance has, as far as can be seen, only a single mike."

and GSS commented
"yes, but sung unaccompanied, by a singer who has learned voice projection,there should be no need for a microphone."

I agree entirely (unless it's the kind of venue where there's loads of noise, in which case I for one wouldn't want to sing there at all).

However, if you do prefer to have an accompaniment, projecting your voice so that everyone can hear it without a microphone is no good if the instrument is just as loud. This is especially tricky with a concertina, because the sound goes out sideways and seems less loud to the person playing it than to everyone else.

That can be one reason for using amplification; not to make everything louder but just to improve the balance. However there's a downside to that, if you get too accustomed to relying on the electronic mix to balance the loudness, and then sometimes sing without the electronics.

Richard