Walmart has a point. CC transactions costs for a store are ridiculous.
If you have a 'rewards' based card, the store gets charged a slightly higher rate then using a card without rewards attached to it. Debit based transactions are usually lower then credit transactions because they charge a flat rate for the transaction instead of a percentage of the sale. In Europe the transaction rates are ridiculously low compared to the US. Here a MC/Visa transaction is anywhere from 1 to 2 percent of the sale. In France it is anywhere from 0.22 - 0.45%.
Smaller merchants, those that do not have the volume to negotiate usually pay a much higher percentage then a place like Walmart.
Visa uses fraud as the main reason on why the rates are so much higher. Going to EMV cards would solve a lot of the fraud issues, but the issuers are fighting it tooth and nail because the cost to make a EMV card is 38 cents versus 14 cents.
An entire industry has been formed because of fraud and it costs software developers a ton of money just to be 'certified' so they can follow the standards that Visa has laid out. Going EMV would all but eliminate the need for PCI and probably make the entire industry obsolete, which is another reason why they are fighting it so much.
I really hope that Walmart wins this case and others follow suit. Maybe it will force Visa to finally adopt standards that will lower the cost of doing business as well as protect us from fraud in the future.