WSJ version
The Wall Street Journal website has posted story bylined by Mike Barris. It quotes the UPS president as saying that while they had recently thought Airbus would adhere to a 2012 delivery date, they no longer felt confident in that (greatly delayed) date. He goes on to cite the diversion of employees from work on the freighter version to the passenger version--implying that said diversion preceded the final UPS termination decision.
Personal comment (mine, not the article's): it seems that at this stage of play neither party was very eager for this order to stay on the books. A costly diversion from the main game for Airbus, and a lonely and uncertain bet for UPS.