NBC Nightly News--Cancelled!

On Tuesday, the Nightly News lead story about the U.S. Post Office was given the on-screen title "Canceled" (apparently Brian Williams and his producers thought this story was more important than the earthquake in Chile). Last Friday, a Nightly News story about the snowstorm that hit the Northeast informed us (in an on-screen graphic) that 1,000 airline flights had been "cancelled". So which is it--"canceled" or "cancelled"? Pick one spelling and go with it. Is anyone at Nightly News paying attention? Does anyone there even care?