The Cincuratos are V rated A/S RFT's with a wear rating of 400. Tire Rack sells the Cincuratos so something smells fishy. Make sure the replacements are equivilient or get really big bucks like thousands for the shorter life. My Tur** from Bridgestone were throw aways after 20K miles - check the 3 series posts on Runflats for details. I just returned from handing over a check for 50 BIG for my he new X3 and this is not good news.
Correction the specs above are for the Cincurato 245/50/18 that is seen on the 3.5 X3. Unfortunately the size you have are only rated at 260 for wear. The tyres are also summer performance not all seasons, which most likely is the reason BMW wants to trade them out.