Very true; but what I constantly need to know is whether any of my build queues are empty -- not what's been finished.  Knowing a building, or several, were finished (but with no visible clue or message regarding where) is of minor interest.  What's important however, is which of my cities has an idle queue that is not producing anything.  Regrettably looking to see if all lines are yellow or whether any has gone black simply offers no clue.

You can see which city has something being built by looking on the left hand side of the screen where the cities are listed, if there is a yellow line then it is building something, a red line means you are producing units. You can also jump to an idle city by using the button at the bottom of the screen (just to the left of the research turn bar).