> On Windows (and mostly in Linux too), I can navigate the entire system, application menus and UI controls without touching the mouse or trackpad, relying only on the keyboard.
At least on Windows, this is for historical reasons: back in the late 80s and early 90s, when the Windows interface was originally designed, having a mouse (or any other pointing device) was optional. Windows had to be fully usable on computers which came only with a keyboard. (There were a couple of exceptions, IIRC the Paintbrush application which came with Windows required a mouse, for understandable reasons.)
At least on Windows, this is for historical reasons: back in the late 80s and early 90s, when the Windows interface was originally designed, having a mouse (or any other pointing device) was optional. Windows had to be fully usable on computers which came only with a keyboard. (There were a couple of exceptions, IIRC the Paintbrush application which came with Windows required a mouse, for understandable reasons.)