Exactly. Their auction says "This system is configured with two of the new ATI 4870x2 video cards available for us to ship after August 12th 2008. ". Not ON Aug 12, but AFTER Aug 12. So they get people to pony up a bunch of cash on pre-ordered 4870X2 systems, then pick up the cards on/after Aug 12th and ship the systems. ANYBODY can do that.
As far as I can tell, they're simply trying to get a jump on other system resellers. Now if they actually had a picture showing the cards along with a little sign saying "shipit!store", then I would believe that they actually have them in stock right now.