"There does seem to be a predisposition to singing in a peculiar nasal style with a non-descript, generic 'Archers' regional accent."

This is very true, but this style is usually affected by those singers who are attempting to imitate their favourite revival
singer(s). It seems unlikely to me that such people have ever listened to a traditional singer - or, if they have, it never seems to have occurred to them that there is anything to learn from such singers. This is a big mistake. Many traditional singers were recorded when they were quite old and I have heard them dismissed as "croaky old gits" and other such ageist drivel. The thing is that their recordings tend to be a world away from slick modern presentations of popular music, including stuff under the marketing category "Folk" (which often has nothing to do with 'real' folk music - see endless 'what is folk?' threads on this board).

After a lifetime of listening to recordings of traditional singers I am convinced that the best of them (Sam Larner, Harry Cox, Joseph Taylor etc., etc.) were great artists and we revival singers still have much to learn from them. If I was asked to define the difference between much modern marketed 'folk' music and recordings of trad. singers it is that the former tend to be obsessively concerned with the overall 'sound', rather than the content, of a song, whereas a traditional singer tends to focus exclusively on unpretensiously communicating narrative and melody. For my taste this is a more satisfying and authentic form of music.