CNBC’s Bob Pisani spoke with Rory Tobin, Head of the Global SPDR ETF Business at State Street Global Advisors, and Todd Rosenbluth, Head of Research at VettaFi. They celebrated the 30th anniversary of the SPDR S&P 500 ETF Trust – the largest, most heavily traded ETF in the world. They discussed why indexing has challenged active management and why ETFs have been such a successful wrapper for indexing – to the point of actively challenging mutual funds as the investment vehicle of choice.