California does not like diesels. Or, more precisely, the people in the government pushing for zero emissions and electric vehicles do not like diesels.

From their perspective, the advantages of the diesel over gasoline simply delays their ultimate goal of electric vehicles, and therefor are an obstacle, rather than a help, to their long-term plans. Diesels, with their improved mileage and performance, provide an attractive alternative to gasoline as compared to the disadvantages of hybrids and electrics. In contrast, they love hybrids, as they see them as a nature step in the development and evolution to electric vehicles.

As a result, I suspect that CARB tends to be rather "picky" and slow with diesel approvals as they want to discourage their development.

As for the 40d, the possibility exists that for the U.S. BMW might skip the 40d version and go directly to the 45d in a couple of years, or even wait until the X5 redesign in 2013/14.