TV movie broadcast shutters, but commercials do not

I'm watching Lord of the Rings on AMC right now, and there is subtle, but very noticeable shutter/frame drop. Interestingly, the shutter does NOT occur during commercials. Does AMC or Xfinity try to save bandwidth by purposely cutting frames from movies? This is not the first time I've had to watch movies with poor play. The smooth playback of commercials shows it is not a hardware problem.