Also for people without a business background: Gross profit is what you charge (Hamburger at Burger King: $1). Net profit is the money you make from it after you pay costs. Burger King doesn't make $1 per burger, since they have to buy meat, ship it to their stores, have it prepared, etc. Losing 3 cents out of every dollar to AMEX instead of 2 cents to Visa/MC doesn't sound like much, but it's huge if you're only making 5 cents per burger.

That's why fast food didn't take credit cards for so long - I hear the CC companies inked deals at lower than normal rates for some huge-volume small-margin companies like Walmart, McDonald's, etc. The credit card companies want more widespread use of their cards so people start using them for everything. As a small merchant, you're not going to get that and it's yucky. It's part of the game right now unfortunately, but that AMEX additional 1% of GROSS is really huge in many industries.