The money I see is in payment processing.

Hmm. They better pass on some of the savings to the customer.
I would guess they are paying 1% on outsourced processing. That is 2% less than they likely pay for outsourcing payment of a credit card and they should, at least, split that with the customer. I have come to expect a bargain with bitcoin because I am sweetening the deal for the seller also. They are getting an irreversible payment within the hour, and saving 3%. Of course I pay the bitcoin fee, but that is a low and fair fee that goes to strengthen my money.