In the NeXT/Mac family tree, at least, it has steadily improved. - The thumb became proportional. - The arrows moved to the same end (so you didn't have to hi

In the NeXT/Mac family tree, at least, it has steadily improved. - The thumb became proportional. - The arrows moved to the same end (so you didn't have to hit another tiny target on the opposite side of the screen when you overshoot by one line), and then disappeared entirely (when hardware scrolling interfaces became commonplace). - They gained the ability for click to mean "jump here" (and option-click to reverse this setting on-the-fly). - They disappear when not in use (to save space), and became bouncy at the ends (to show you more clearly when you're at the end). Not every OS has improved their scrollbars in the same ways, but most other OSs have proven themselves not-quite-competent at understanding (and copying) the state-of-the-art in GUIs. Windows 1.0 was terrible at everything, not just scrollbars. That's not an indictment of this process as evolution.