It's not just U.S. airlines... I flew Varig to Brazil, a great airline by most standards. While in Sao Paulo awaiting our flight to Miami, we were informed the plane had mechanical difficulties, and we wouldn't be able to fly until the morning. They ushered us out to the public transportation lanes and issued taxi after taxi a voucher to drive us to a 4 star hotel that they contacted and requested they hold the evening buffet open for the passengers, as it was quite late by that time (after 11:00pm). In the morning, two beautiful tour busses (nice and clean and new), complete with air conditioning and full bathrooms, picked up the passengers at the hotel and brought us back for our flight.
Needless to say, every single person on the flight missed their connection in Miami. Keep in mind this is the SAME airline, just in Miami instead of Sao Paulo, Brazil: The plane got in fairly late (I don't recall exactly what time... but late evening at the earliest). No one was there to meet the plane and make arrangements for connecting flights. No one was at the desk. We had to call the airline in order for them to get someone to come and deal with us. They arranged our flight for like 6:00am the following morning, and told us we could go to a particular hotel (decent, not great hotel), and we needed to catch the hotel's shuttle in the public transportation area. So there we were, like 150 people waiting the the curb... with all of our luggage, and the bus pulls up, the driver opens the door and says "I'm sorry, I can't take all y'all," and drives off without taking anybody. So we go back to the Varig desk to complain (yes, the shuttle bus should have taken people, but it would have taken 10 trips to get everyone on their luggage anyway). They called the hotel, but would not pay for taxis or arrange any other transportation. I ended up just taking a taxi at my own expense anyway. We get to the hotel and it's jam packed... the check in line was out the door. Many people didn't even get a room until 4am, enough time to take a shower and go back to the airport. In Brazil we walked into the hotel and were just handed the keys to a room, the airline had taken care of everything; everybody had a room in, I'd guess, no more than 20 minutes.
The conclusion is the airlines don't have the onus in the U.S. that they have elsewhere to treat passengers better. Why the amazing treatment in Brazil? Are there laws about it? I don't know. We made Varig aware of our dissatisfaction and haven't used them since, but what else are you going to do? You're usually limited to flights available, there isn't always a lot of choice.