Canon likely has a overstock. The D800 has been seeing big discounts on ebay as well.
The reason is simple. Worldwide, the economy has slowed down and sales of luxury items has dropped. Canon likely gave Adorama a sweet deal if they would buy a couple million dollars worth of cameras, but they do not allow Adorama to advertise them below Canon's guideline prices. So, Adorama has had a longtime presence on ebay, and they are blowing them out for a few dollars each profit. Even at $100 profit each, they can quickly convert them into a bit of cash in short order. Chances are that they get a big ebay fee reduction for the deal as well, so they are not paying 2.8% like I do.