I always remembered the original saying is that human will consider things "animated" when it's above threshold (24fps or whatever).

Telling 24, 30, 60 apart is very trivial.

As for 120fps, you need to keep in mind that playing a real-time rendered computer game is a totally different beast than playing back a steady video. There are lots of other factors involved. Some headroom in FPS makes lots of difference due to various other things like jittering (judder?), input delays, response time etc. (also it's possible some people simply can tell 60/120 apart, even by just watching a video.)