There is no 120Hz content so the panel runs at 120Hz and used the extra for smoothing, that soap opera effect and to support 24p mode.

http://www.samsung.com/us/support/owners/product/LN40C610N1FXZA in it's FAQ writes "The processor on the Samsung 120Hz/240Hz units will always display at their respective Hz. Even when the signal is only being transmitted at 60Hz, it will always display at 120Hz/240Hz since the processor is always upconverting the signal. Activating the Auto Motion Plus feature will allow for judder reduction and blurring reduction, depending on what settings you activate. This will enhance your 120Hz/240Hz viewing. The reason you are seeing the 60Hz in the info box is because the info box only displays the signal???s actual Hz and screen resolution and not the info of the picture on the screen after the TV processes it. Meaning that the 60Hz you are seeing is the signals actual Hz and not the screen???s Hz. Currently there is no way to display the screen???s Hz in the info box. -MrSamsung"