> but I think interest versus merchant fees was about a 67%-33% split in terms of credit card company revenue. (American Express is an exception because they do not allow you to carry a balance on a lot of their cards; they will report your account as delinquent and terminate service

That's correct. Depending on the issuer, it tends to be around 70% interest revenue. Pretty much all of their profit comes from this though! Amex does allow you to carry a balance but their ratio is opposite of others 30/70%.