It's the ad valorem impost that gets me. 2.5% on $700 is much more ($17.50) than 2.5% on $100 ($2.50) and yet each transaction takes the same amount of effort to process electronically. If I have the time I'll pay by cheque and put the cost back on the merchants. One day they'll realise that it would have been better to absorb the transaction costs instead of paying higher wages bills.
A cheque for $700 or $100 costs the same amount for the business to process (ie. the trip to the bank plus the time for the staff member to record ID). But an Amex purchase of $700 would cost the business much more (eg. $17.50) than a $100 purchase (eg. $2.50).
It is the credit card company that you should be annoyed at - not the business.