There are a lot more voters w/o 401Ks than with and I bet there is a racial disparity too - eat the rich as they say
You have to take into consideration pensions. They are all invested in the stock market. Do you really think their are more "likely voters" that have no vested interest in the stock market (401(k)s, IRAs, stock ownership, company ESOPs, stock options, pensions, mutual funds, etc.). I'll bet dollars to doughnuts, the reason people have traditionally pulled the lever as James Carville said, "its the economy, stupid". The main reason for that was both employment and the stock market, and one goes hand in hand with the other. The stock market (returns on investment) is king.