"They differ from what is generally considered gambling, however, in that the expected return on capital is positive."

I wonder if that isn't partly illusion. The expected return is based on prior performance and that usually implies a reliance on long term indices, such as the DJIA, NASDAQ-100, and S&P 500. However, these indices are all biased; first by the fact that they are not inflation adjusted and secondly, and perhaps more importantly, they are cherry-picked: bad performers are, by design, removed from the averages and replaced with rising stocks. Thus, growth in these indices is forced and unrealistic. Many of the stocks at one time included in the DJIA are gone - in some cases by bankruptcy - so that their stock value is really zero. I think a lot of the positive expected return is wishful thinking.