Are you saying Credit Card's do not charge the stores a fee when used? I'm pretty sure, and I intend to look it up. If they do then obviously any company is willing to reduce the amount they charge you by some amount. I've never heard of it as the companies doing shady stuff... I will look it up.

Edit: Did a quick search and a bunch of sites are saying what i'm saying. I already know for a fact that credit cards charges the company every time a customer pays with one, because and aquintance refuses to accept credit cards at his business for that reason. I think he's foolish as it turns away more customers than anything, but that's his deal.