> banks whose shares are often packaged in index funds tend to offer higher fees and rates for such services as account maintenance and deposit certificates than banks whose stocks are rarely or never included in index funds

Obvious explanation: the banks packaged in index funds are the largest banks. People don't tend to switch banks all that often, so larger banks charge larger fees to take advantage of their existing customers whilst smaller banks offer better deals to get customers. The explanation in the article makes no sense; it's in shareholders' interest that the banks they own shares in make as much money from customers as possible. (Also, since either outcome could be used to justify their conclusion, this is not science.)