Comment 7 for bug 368962

The severity is a matter opinion, but if several users feel it is severe to them, it qualifies as High, as per the provided link.

As for 'no portable way...to reboot...', most (if not all) OS's respect ACPI.

And, in a similar vein, if you can walk up to a physical machine, most physical machines will gracefully shutdown when the power button is pressed, so I don't see your point #6