[bill_from_tampa]

I suspect this is more complex than just frontrunning. An article from the Fed Reserve Bank of NY from 2011 discusses the whole process of being listed on an index. Firms selected have been outperforming the market for several years at least, and their metrics have been improving even before selection is announced. This may be why these companies were chosen to replace others that are failing.

The Fed report found that there is no long term impact of being chosen to be on an index.

http://www.newyorkfed.org/research/staff_reports/sr484.pdf