IMO, the primary reason for this is because WCS is danced to contemporary music. When the music changes, the dancing changes to suit it. I think your example i

IMO, the primary reason for this is because WCS is danced to contemporary music. When the music changes, the dancing changes to suit it. I think your example is actually quite illustrative of this - the 2nd song had a lot more "swing content" than the first; since it's an older blues song the traditional West Coast Swing patterns fit it better.