Ithink ther is something in JohnAdams post and also in Pirandellos.
good TRADITONAL SINGERS and also good BLUES SINGERS,managed to convey feelings and emotion,almost certainly sang the song differently each time without thinking about it,it was something that occurred naturally.
It is possible to teach singing technique and style and this is praiseworthy.but singing with feeling is something that has to come from inside,some people have it, some dont.
Futhermore some people can have it one day but not the next.the muse can be fickle