Let’s say you click on the volume icon in the Mac system menubar. Now, keeping the cursor on the icon, scroll up to increase the volume. The catch is, you can’t.
While the scroll direction of the volume slide really is the natural direction, only the dropdown slider accepts scroll events. The more convenient interaction is to extend that area to the icon so that it is possible to change the volume without moving the mouse.
Yes, this is the smallest nice-to-have feature, but why not?