Well this is also because we have these Bridgestone RE050 which are only rated 140 for treadlife... The same tires in non RFT are rated the same but have the reputation not to wear as fast as RFTs. I do not know how long they would last though. For reference the PS2 on my 330CI of the same size are have a 220 rating and last me about 20k.
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