[earthsaver]

Are you saying you want the tab drawer to close when you only have one tab open, to dynamically remove/disable the Close Tab command in the Window menu, and to dynamically change the Close Window command to Command+W.

Other than that, I think the behavior is perfectly intuitive as long as you can clearly see that there is only one tab open and therefore closing it will close the window. Further, you can tell there is only one tab open by the lack of a dot in the red close window widget; it only appears when there is more than one tab open, thus presenting a dialog confirming window closure that would lose multiple open tabs.