Putting window buttons on the top left actually makes sense. GNOME's HIG (which Ubuntu primarily uses) says the "action buttons" (OK / Open / Save / "do something" ) are supposed to be put at the bottom right of the window. So, in contrast to these buttons, the ones that control the window itself are put at the top left.

Thanks to that, I'm often not even looking at the buttons themselves if I want to open something; I just click the one at the bottom right and I know It Works ™.