I think as you say there is a subtle distinction. In the case of an exogenous event that tanks the entire market, you have to make a value judgment, ignoring existing shareholdings. At Sept 11 my wife and son both held QAN bought at higher prices. However it seemed a no-brainer to buy more in a depressed market given the circumstances (Ansett collapse). I didn't/don't consider this an average down although in a mathematical sense it was.
