Jeff,

Thanks for pointing me to m3forum.net.

One poster there said the following about the rotor differences
between Europe and US:

***************************************************************
1) Fear of how easy it is to sue a manufacturer here for product
liability. BMW's lawyers were nervous about possible liability
concerns. They were worried that some owners would use the
cross-drilled rotors too long (well past their wear thickness rating)
increasing the possibility of the rotor cracking between the holes.
That could potentially lead to the very remote possibility of
catastrophic brake failure. (and the subsequent lawsuits blaming BMW
for this) The poor maintenance reputation we have in the U.S. (at not
being diligent about performing routine inspections on our cars) is
something I heard before from other manufacturers as well. It seems we
are somewhat 'marked' in that regard.

2) Cost - Euro-spec rotors have a two-piece 'floating' construction
that is more expensive to manufacture. The aluminum hat (instead of
CAST IRON) uses steel pins to mate to the outer cast iron friction
ring. This type of rotor effectively doubles the manufacturing cost
per rotor, so a cheaper but still effective alternative was selected.
(100% CAST IRON solid rotor) Also, U.S.-spec M3's had the lowest base
price point of any E46 M3 in the world. Our U.S.-spec E46 M3's are at
least $10,000USD cheaper than any other world market. That
significantly reduces the profit margins on those cars. Volume sales
only cover a part of that deficit. You have to remove some standard
equipment (making them optional), and manipulate a few other things in
order to make the much cheaper base price financially feasible.

3) Noise - The cross drilled rotors make a distinct noise as the air
passes through the cooling vanes and the cross drilled holes at lower
speeds. They also create a sound based on how the edges of the brake
pads interact with the edges of the drilled holes. This noise is very
irritating to some individuals, and it was determined that the solid
rotors would not produce this noise problem.
***************************************************************

What was said in item 1 & 3 seems reasonable.  What was said in item 2
about cost is anybody's guess.

G.S.