I have noticed that the fabbers seem to use these terms interchangeably but I always thought the term frock was a looser fitting garment as it references the frocks worn by the clergy in the days of old and that dresses were the more fitted garments worn by ladies in the courts of the 1700 and 1800s.
http://en.wikipedia.org/wiki/Frock
Is there a difference between a frock and a dress or is this just a regional dialect preference?