It actually is more like $200mm gross (due to discounts, and that's run-rate, not 2012 I think), and then goes to Chase Paymenttech and to the card associations, interchange, issuers via chase -- as well as all their other costs. So I think netting $50mm off the transactions is generous.
They have at least 500 employees -- figure $100k/ea loaded cost, only possible since I think a lot of those employees are not engineers. That's all of it right there.
They really need to be in the 50b/yr range to be doing well. OTOH, they will probably get there in a year or two, and I don't see their costs going up much.