I don't honestly know if there is a command to make that window appear, there are separate commands for shutdown, reboot, suspend and the like (most of them are located in /sbin) but that is not what you want I think.
There is one solution that I know of and that is to switch desktop managers. I presume you are using the default Gnome, if you switch to Xfce (which is better btw
) then all you have to do is right click the desktop to be able to access a shutdown menu.
A workround that I can think of is to add another panel (auto hidden) at the top/side of your desktop and add a standard start menu to that.
I actually use both of these methods because as you say AWN, amazingly, doesn't seem to include a shutdown option.
Fujitsu Lifebook AH532. Intel i5 processor, 6Gb ram, Intel HD3000 graphics, Intel Audio/wifi. Realtek RTL8111/8168B Ethernet.Lubuntu 13.10,Ubuntu12.10 (Unity), Mint16 (Cinnamon), Manjaro (Xfce).