In the OP's case, it appears that US was in breach of regulation EC 261/2004
from the very start by not informing PAX of their rights under EC 261/2004.
Article 14
Obligation to inform passengers of their rights
- The operating air carrier shall ensure that at check-in a clearly legible notice containing the following text is displayed in a manner clearly visible to passengers: ‘If you are denied boarding or if your flight is cancelled or delayed for at least two hours, ask at the check-in counter or boarding gate for the text stating your rights, particularly with regard to compensation and assistance’.
- An operating air carrier denying boarding or cancelling a flight shall provide each passenger affected with a written notice setting out the rules for compensation and assistance in line with this Regulation. It shall also provide each passenger affected by a delay of at least two hours with an equivalent notice. The contact details of the national designated body referred to in Article 16 shall also be given to the passenger in written form.
- In respect of blind and visually impaired persons, the provisions of this Article
Here's a poster:
http://ec.europa.eu/transport/passen..._apr_a4_en.pdf
And a Leaflet:
http://ec.europa.eu/transport/passen...leaflet_en.pdf