You often see the cutting edge of financial innovation in the latest trends in the exchange-traded fund universe. Whenever someone sees a potential new angle on a successful investment, it likely that a new ETF will appear to give investors a taste. That's what initially happened with the Invesco S&P 500 Equal Weight ETF (NYSEMKT: RSP), which was designed to take advantage of potentially market-beating returns from weighting the smaller companies in the S&P 500 the same as the larger companies. To date, ...