Why would BWM spend $500,000 on new tooling and engineering resources to make a US Spec air box?
My guesses:
1. to make the car quieter for US tastes.
or
2. to be able to use a flat fiter so that the flat carbon filter can be installed to pass USA emmissions.
or
3. because they like to spend money on engineering and tooling for fun (hey, they're German
).