Perhaps you shouldn't make such assumptions--for example, in a portfolio of over $1 million, one can easily make 120 trades per year without it 'costing' money in the long run...

I don't think anyone should be making 120 stock trades per year. Commissions, the bid/ask spread, your time, and taxes add up. If you've got a $1MM portfolio, I hope you've got a diversified portfolio of 15 stocks, and have a turnover or 20% or so- that would be 3 trades per year.

Everyone I know who made millions in the stock market did it by buying and holding for the long term and keeping costs down.