I am most definitely talking about debit cards. I said "fee for charging a debit/check card". They make up 25% of my online processing volume despite being a mostly B2B business. They're probably more than 25% of Stripe's volume.
Whoops, you did say that, way back in the first post in our thread. Sorry, I've been focused on credit cards — all is clear now. I hadn't thought at all about that wrinkle of Stripe.
I suppose it's (only partially) balanced by the higher AMEX, etc fees.
Visa interchange fees: http://usa.visa.com/download/merchants/Visa-USA-Interchange-...
A screenshot of a transaction report at my processor: http://i.imgur.com/fSycwUS.png
Feel free to e-mail me if you'd like any other clarification or information. It's in my profile.