Well, most of this sub 150ms lag everywhere in the interfaces is actually artificially designed, and believe it or not, some people do prefer it like this, so it's being designed like this. I'm personally for making everything as fast as it would be, but for most people it really doesn't matter.
So you're saying there could be a designed behavior that I misinterpret as a lag? Sure, but unlikely (rarely), because I'm quite perceptive in this regard as I programmed a lot of GUI myself. If I press a button and an animation starts after a while (sometimes in javascript after around a second!) then it's not by design. Similarly if someone is bad at optimization but not as bad and the animation starts after ~100 ms.
I am aware there could be something like a non-linear alpha animation, and so there could be a period of time where the alpha is so little, and it accelerates so slowly, that I could miss the first 100 ms of it - but then again because I'm experienced in gui programming, I would consider that.
For the most part people are just bad at optimizing gui, especially in HTML.