Verizon recently made headlines by saying that it would charge customers a $2 convenience fee for monthly payments made over the phone or online. This created such an uproar that the combination of online petitions, national media attention, and the involvement of the FCC made Verizon turn 180 degrees and rescind the fee. Certainly McAdam would have been inundated by the press during the show, asking him about what went on in the decision making process to first ask for the free, and then to cancel it.
Additionally, Verizon's self-proclaimed "most reliable network" had some problems last month when its 4G LTE network went down three times in a matter of weeks. And while the company's CEO will be off the hook because of the schedule change, whomever is sent to replace McAdam at the show will be on the hot seat while the show is open from January 10th through the 13th.
source: Reuters via AppleInsider