I am not taking US' side since I am no longer a US FF, but the weather problem was in fact true. See this thread: http://www.flyertalk.com/forum/us-ai...er-waiver.html

I figured a lot of flights reached their destination very late that Saturday night/early Sunday, if not cancelled. So the crew rest problem could be due to the weather. I spent 7 hours on CLT tarmac before the flight was cancelled forcing me to spend the night at CLT terminal, and I got nothing from US but being rebooked on the next day's flight.