strange, i can only suggest your screen my have been in 60hz mode and not switching to 120hz because it`s even noticeable the first time you move your mouse or move some windows around.I`ve sometimes had games that leave the screen in 60 hz mode despite selecting 1920x1080.Also i assume your graphics card had the power to play stuff at 120 fps.
One thing 120hz screen`s most certainly are NOT,is the emperors new clothes.
Don't hold your breath. Certain limitations mean that we may never see that kind of technology adopted for PC monitor use I'm afraid.
Managers Post:
LGs transition from LVDS to DP interfaces will see a new line of displays emerging this year with 3D and 120Hz IPS in the pipeline.