To be more precise it is characteristic of TVs that have a frame interpolation option, such as 120Hz or 240Hz LCDs. It is not because of the TV being 120Hz in-and-of-itself.
I agree that it’s really odd looking and distracting, especially for film content. A lot of lay people seem to love how smooth it makes everything look.
When you turn it off your TV will just repeat frames to get up to 120Hz/240Hz, keeping the same cadence as the source.
