Regarding "chords following em": Since all of the songs were transposed to the key of C, em == iii, am == vi, and F == IV. Really what the post says is IV and

Regarding "chords following em": Since all of the songs were transposed to the key of C, em == iii, am == vi, and F == IV. Really what the post says is IV and vi follow iii most often in popular songs.