You have been driving on very smooth german highways. Not on the grooved pavement here. From what I can see on Tirerack, people get 15k at most with these tires.
2000 Z3 2.8 TiAg (retired)
2002 330i Orient Blue (retired)
2005 330Ci TiAg (retired)
2009 Z4 30i Space Gray (retired)
2011 Z4 35is Space Gray
2011 535i GT xDrive Space Gray