I watched the video and read a few articles on Manning leaving the field without shaking Brees' hand. His comments were:
“The stage is being set up for the celebration and it was time for the Saints to celebrate at midfield,” Manning said. “They deserved the moment.”
and
For the record, Peyton did call Brees later in the night. Said the Saints quarterback: "Peyton's a class guy."
From the video, it looked bad. He (and Reggie Wayne) both left and it looked bad. I guess, for me? It just doesn't ring out as loudly because Manning didn't mug it up so blatantly and abrasively all season long leading up to it. Newton makes it easier to hate him for that reason. Oh, and when it came to the press conference in 2010, here's how Manning handled himself.