The additional AutoMotion Plus processing is likely what is causing that "smoothness effect". Most customers who find that effect bothersome remedy the situation by adjusting the AutoMotion Plus.
Since you noted that you also watch movies (since movies can come in through both the same box as the TV, or on a different input), you CAN set AutoMotion Plus settings by the input. So each input has its own set of settings that you can individually select for that device.
Motion blur can depend on the broadcast, the resolution being broadcast and the processing. It can also be dependent on the panel in some cases, but your panel will upconvert to 120Hz anyway - and that is specificially designed to reduce or eliminate motion blur by its very design.
Let me know if you have any further questions.