Smileyman, as you can see from the thread, different people will give different answers to these questions. But specifically with tegards to yout first question (is it the song or the singer), my personal view, following from my "folk ethos" argument in my previous post is:

The song can be folk because it is written with a "folk ethos", and if performed in a manner outside that ethos, this doesn't stop the generic song from being folk - but the performance is not folk. A folk song sung in a non-folk (pop, rap, whatever) manner, that's all.