Alex (and NOT me, thank you very much!) can testify to the speed limits and other related laws (such as no tailgating) do in fact exist on the German Autobahns!
Very rarely will you see a Polizia pull over a car for speeding, or anything else for that matter. BUT you do see cameras set up in random spots along the autobahn to catch you speeding.. and as Alex recently found out, tailgating. Often times, you'll see the camera flash overhead, but apparently, that is not always the case, for Alex recently received not one, but TWO tickets in the mail, and he didn't even notice being 'flashed.' The first was a speeding ticket for 20 km over the speed limit. The much, MUCH more expensive ticket was for tailgating - a series of 8 to 1o up close and personal pictures of A riding on a bumper.
And now, 360 euros later..