The BMW website is showing $900 for the 2010 model. It makes no sense, but I sent an e-mail to BMW NA and they implicitly confirmed it. I am still hoping that it is simply a web mistake.

The only reason I can think of as to why it has been halved, is if the Government somehow reclassified the X5 into another class or something.

If you search, there are at least a couple of message threads discussing it in some depth.