DISCLAIMER: Expressed views on this blog are my own.
I remember when people said this in order to justify 30fps games and 24fps videos. Yet when a 60fps video comes up on Youtube, I always always question if it is 60fps and see that it is. The fps difference is absolutely perceptible.
There is a significant difference in smoothness. I think people who claim this B S are just fucked in the eyes. 60fps to 120fps is also perceptible, but that's because once you've gotten used to 60fps you can see the difference between that and 120fps.