I can understand the concerns here, but I think they're unfounded, myself. Working in the service industry, I had access to the monthly and yearly P&Ls (profit/loss statements), and I saw how much these companies charge you to be able to accept credit cards.

For a restaurant doing $2 million in sales, these charges were quite high, and they cut into your profit margin by quite a bit. It's almost not worth accepting credit cards, that's how bad it is. So I can fully understand Wal-Mart wanting to set up its own institution to knock the middleman out of the way. Can you imagine the fees they have to pay on credit card processing charges each day? Each month? Each year? Yikes.