TDI Update – unsafe speed(ometer)?

I am still very happy with my new Jetta TDI.  The gas mileage has stayed above 45 MPG consistently, even when I was driving it a bit harder (got the change to go on some twisties near the house and ‘used’ the transmission a bit more than that brakes).  The interior is very comfortable and the trunk has been adequate.  I really can’t ask for more for a fun to drive 100 mile a day car.  However, one issue did crop up in the last week (actually it’s been there all along..I just noticed it last week): the speedometer is way off.
I happened to notice when after I dropped my daughter off for school and they had a radar speed sign at the gate (you know, the ones that tell you how fast you are going with a posted speed limit right there).  Although my speedo read out 45 (the posted speed limit in case you were wondering) the speed sign gave me credit for only 41 MPH.  Later in the week I ran by a similar sign on the expressway and it gave me credit for 65 MPH (the posted speed limit) even though the speedo was north of 70 MPH (so yes, while I thought I was breaking the law, I in fact wasn’t ;-)).
I guess it’s no big deal (like always having a clock that’s 10 minutes fast), but it does surprise me a little given how much the Germans are prided on precision engineering.  Then again, if that’s all I have to complain about after 1 month of ownership I guess I should consider myself lucky.