"Used the way the OP suggests (which is how I tend to use it) it describes the context in which they sing the songs and which shaped their approach to singing."

Yes, precisely, and also the contest in which the songs were created - in fact I was thinking about staring a thread about this but chickened out.

I think Ray has actually simplfied the matter.

OK, here's my Eureka moment coming home on the train tonight (no beer was involved). The songs are like an ancient oak standing in the corner of a field where a crop of fresh new corn is sprouting. They both spring from and are nurtured by the same earth, in the same place, and thrive there. I could go on and talk about harvesting with a scythe or a combine but I really do need a glass of wine or three.