[maxmcd]

I believe in the united states it is simply against the terms of service of the card provider. I imagine the law isn't "allowing" customers to pay processing fees, it's simply preventing the provider from setting those terms.

[toomuchtodo]

No longer true. Merchants can charge CC users in the US a surcharge.

[slice_of_life]

Is there a current book that you can recommend to understand this very arcane business of credit card processing?

[toomuchtodo]

Unfortunately not. Online resources, experience, and payment processing consultants are the options available.