AirTran has switched me to Delta several times. When I emailed customer service, they also gave me full AirTran credit.
They won't move you for weather or pay for hotels for weather. I've gotten stuck before 9/11 and Delta / AirTran paid for hotels for weather. Since 9/11, no airline has put me in a hotel for free for weather.
It's a new economic reality. If you drive and get stuck in bad weather, will your insurance pay for your weather? No . . . it's on you. Same now with all major US airlines.