So if I understand correctly, you're saying it's doubtful a TV with a 120Hz panel will accept 120Hz signal from a PC?
A 120Hz TV is not using any special "120Hz" panel.
The panel has its pixels changed at intervals. It takes time to go from one color to the next, usually several ms.
The video signal is a stream of of pixels of a frame, from top to bottom. A TV typically reads this at 30FPS.
The LCD driver reads the frame into memory, and updates the pixels to match it. However, it can change the values of pixels faster than that. It likely cannot process incoming HDMI or DVI video streams any faster, though.
A 120Hz TV is applying processing to the incoming signal to interpolate between frames and make up intermediate frames. So, it takes in 30p or 60i and figures out the points in between those frames to try to make smoother motion, by displaying more frames. They often do not use any faster panels than other TVs.
A 120Hz PC monitor takes up to 120FPS of input video signal, and displays it. Doing so and looking good requires a fast panel. A complete non-marketing-spec gray-to-gray time of 8ms or better is needed to make 120Hz
really work.
As a bonus, most 120+Hz monitors are made as gaming monitors, and have very low input lag, where TVs often have high input lag, on account of being made to perform a bunch of processing to the video stream.