For real though, 120 is nice even just for navigating UIs smoothly. On top of that, 120 is a nice multiple of 24, 30, and 60. So the device can just output 120Hz and skip frames as needed depending on the source content frame rate.
ie outputting 24/25/30 is completely fine: tv will use corresponding multiples of frames by itself (120 for 24, 50 and 60 for 25/30, etc.)
Maybe at some point I could play games on the Apple TV that do?