My BMW replacement rotors (from my dealer) came with a silver rust-resistant coating on the hub that my original OE rotors didn't have. The box was labelled with the details of the coating, and noted that it was new. Don't know when they changed, or if it is just replacement rotors, not originals. They never showed any rust while I owned them.

__________________
2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue