The People's Key? In my experience that's always the term applied to G. That's what Alex Campbell always called it. Of course it didn't mean he always stuck to it.

Capos give you all the keys - but they also allow you to use all the different fingerings you get to use with the whole range of chords - which makes it much more interesting, especially if yo're playing with another guitarist. So you play in G, but one of you capos up and uses D chords, and it sounds far better then if you're both playing the same shapes.