The rules are exactly as I wrote it
Superflyer, your ticket is more complicated. You are flying with US in economy and then connecting.
So for US airways you are a non international passenger in Economy, why should they give you the same allowance as you will have later on by Lufthansa? If you booked all on one ticket, then you are a international passenger and thats just a feeder flight. But US might look at you as a Eco. international. In such a case there is no clear rules. Every agent on the phone will tell you something else. The check in agent at the airport might decide diffrently, as long as you have nothing in writing, the checkin agent and her supervisors decision is all that matters.