power cords don't have to be distorted, they sound alright even when they aren't overdriven, but the majority of songs that do use powerchords do distort them just because they sound better. if you distort a regular chord it probably won't sound as good as a distorted power chord. I don't believe a powerchord is a substitute for a regular chord, or a regular chord is a substitute for a power chord, they serve different purposes. i'm sure The Offspring, or Metallica could use regular chords if they wanted to, after all they've been playing for over 20 years and have dedicated god knows how much time to jamming, but powerchords sound awesome, and regular chords sound nice.