The left and right <windows> keys are functionally identical anyway, and the <menu> key is functionally identical to a right mouse click.
It's handy, though, for people who cannot use a mouse.
(Okay, so <Prt Sc> is used for "screen capture to clipboard" but who needs a button for that?).
I use it all the time. Saves buying screen capture software.
They could have just used, for example, <Scroll Lock> for <windows> and <Pause> for <menu>, without then having to scrunch up the <alt> and <alt-gr> keys and shrink the space bar.
With this I agree, and the keys could have retained their meaning in DOS windows. Perhaps the older versions of Windows weren't up to the task.
Vaguely ob Unicode, SC Unipad has keyboard layouts for many languages, but has the euro at Alt-Gr w on the "English (British)" keyboard.
-- Curtis Clark http://www.csupomona.edu/~jcclark/ Mockingbird Font Works http://www.mockfont.com/

