The red lights that follow the needle around the speedo face on startup. What else are they used to indicate, if anything? And why are there no corresponding lights on the tach if these are purely decorative? Am I missing something obvious?

 

The lights are used to display the difference between your speed and the car in front of you if you have Distronic activated. See page 201 of the US owners manual.

If you don't have Distronic, then they do nothing.

 

OK, got it! I thought they were just for entertainment while waiting for the music to come up to volume.