I really don't want to get too involved with this one but IB's fees include SEC fees, exchange fees, ECN fees, etc. In particular, as one does more size, the SEC fees really add up. IB is eating them. The firm also doesn't charge for half the things other firms charge for (bank wires, option exercise/assignment, order cancellations, software, DVP, ACATS, etc). There also is a huge cost to maintain the global networks and infrastructure. Not to mention personnel, insurance, R&D. The speed of the TMBR route alone is probably worth the commission. With that said, I believe the IB deal is competitive with anything out there and I don't see rebates in the picture any time soon.