I could only find this...
http://cfr.vlex.com/vid/122-165-air-cabotage-19649356
And it states passengers, any property or mail for revenue. I'm not really up on Cabotage laws....if you could, could you post something that shows the exemption for cargo..
Your link is correct.They cannot carry revenue between two stops in the US. They can however stop to pickup freight or PAX's that's destination is outside the US .