I've been thinking more about this.

What I've picked up so far:
1. The US market is the only location with the old 6 speed diesel for 2011 (maybe Canada too?).
2. The 35d was delayed getting EPA/CARB inspection - I suspect BMW made some last minute changes to cause this, like getting a US emissions surprise on the 40d.
3. The 40d has better hp, torque and mileage (8 speed transmission).
4. bmw.com (the international site) doesn't even mention the X5 6 speed or 35d anymore. the 35d must be on the way out.

I suspect BMW ran into trouble getting the 40d ready for US 2011 launch so changed it out for the 35d for now. The question is - when will they switch to the 40d and make the 2011 35d a less desirable car in the US market. In model year 2012 (September 2011) or some time before then. Seems doable unless they don't want to deal with a mid model year change. Any historical precedent for stuff like this?

Conspiracy theorists apply here.

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1995 BMW M3 (Track prepared)
2006 BMW 530xi (Wife)
2011 BMW X5 35d (Tow/Daily)