Nope, I have seen that happen first hand. I will ALWAYS book direct through the airline after seeing a weather related cancellation while flying on American.
Person after person were told to contact their booking agent for rebooking, American wouldn't do it. Fortunately I had booked direct on American and they rebooked me straight away. But it left a ton of people clammering for there cell phones to call expedia, Orbitz or whoever they used for the original ticket.
Quite a sight........