the link didnt work for me, but i think your talking about barre chords. in a barre chord you have to lay your index finger across all the strings in the chord even if your playing higher notes on some strings. this is because its a lot easier that way instead of trying to keep your index finger touching only the strings it plays. i dont think that made any sense, but try doing the fingerings the way the charts show it, then try doing the fingerings with only one finger touching each string and you'll find its a lot easier the way the charts show it. i know basically nothing about theory, but power chords are basically a section of a chord, only the 1st and 3rd or 5th notes of the scale, i dont know which it is. power chords sound better on distorsion than full chords becuase theres less notes, the full chords w/ distorsion have too much sound and sounds muddy. and on a clean sound, full chords sound better than power chords.