I always wondered why they chose a minus sign. Now I know that they didn't! lol
If the system menu is there for mouse-less window manipulation, then I think it can safely be removed. What computer doesn't have a mouse these days?
In fact I had to use this just the other day. The Cisco VPN client window was open on my second monitor. When I disconnected that monitor it still believed that was where it was and was therefore invisible.
I had to do a Shift + Right click on the task bar then use the arrow keys to move it back onto my laptop screen.