I'm with you on that, I can distinguish up to ~100fps pretty easily but above that I can't tell any more.
Here's something interesting, if you're just watching a game can you see anything above ~60? The only way I can tell is how the game responds. I've been trained that ~100fps is "normal" by all the fps games I've played over the years, anything that *ever* dips below 60 makes me perceive the game to be running "choppily." I guess I'm spoiled, lol.