Earlier quoted context omitted.
Elements on the top of the screen have virtually infinite height, and elements in the corners have infinite height and width. You can't aim "too high" for something at the top of the screen. Status bars on top don't make sense if you have tabs on top. Now your tabs are infinitely smaller, and aiming at them requires a lot more effort. Mac's original design had the menubar on top, and its windows didn't have tabs, so…
I wonder how relevant Fitt's law is with bigger screens and the drastically changed ratio between mouse hand movement and cursor movement on screen. It used to be that you could reach a screen corner with a very simple flick of the mouse hand wrist. But that doesn't feel the same way anymore on modern hardware.
On my laptop's FHD screen it's even better.