It's the reverse here. Around 3-4 years ago the state "outsourced" all the credit card payments to a third part, whose cost you 100% incur. The good news is it's reasonable (2.something) and now credit cards are accepted for just about every state government transaction.

There is a trend though for the credit card companies to offer "special" processing rates to certain emerging markets that they don't traditionally have a stronghold in. Sometimes they are very aggressive (ie:1%).
Things like:
Utilities (mandatory -- power -- water -- not entertainment: Cable/TV which get charged a high rate).
Education/tuition
Government services/tax payments.

Finally, one oddball one is grocery stores have always been low. I don't know the history on that, maybe its just low margins, but the grocery store rate is ridiculously cheap compared to other merchant industry codes.

A little off topic but one strange one was the US Government GSA. They used to take a CC for anything. You could buy 10 cars from them at an auction and put it all on your AMEX. In the last year they've limited it to $49,000 per 24 hours, but still... it's an oddball.