Is there a way to simulate a “Close” event on various windows using the terminal?

I answered on Ask Ubuntu Quit all instances of gnome-terminal via a command but as you all can read gnome-terminal didn’t seems to have a SIGcall I could use to simulate this “Close” event. So this lead me to ask, is there a way in GNOME/KDE/LXDE/{put your window/desktop manager/environment here} to simulate the “Click in close button” event? I have read different questions that could have any relation to this, but don’t answer this.