Sometimes HD games are in 5.1 audio, and sometimes they skimp and do 2.0. With that said, it sounds to me you might have a local channel broadcast issue. I watched that game, and it was in 5.1 for me.
My local ABC station sometimes fouls up their audio in similar fashion. Sometimes they'll broadcast live HD-sporting events in such a way that audio comes through the fronts, but with no center speaker audio
Then I'll call my brother who lives out of state (who is watching the same football game) and the audio will be in perfect 5.1 at his end. We both use direct-TV SAT, so the local broadcast feed gets the blame.
For me, if there is ever technical problems with the audio, video, etc, etc, etc.........my local ABC affiliate is the slacker who screw it up. Never anyone else......
Maybe in your local market......the folks at NBC are the slackers