Keep in mind this was presented in October. Look at the bottom.. October 2010, and an NDA of 11/22.

Most likely the specs were hidden so Nvidia wouldn't get the leaks. Flash forward to the 6990 slide posted a few pages back, which had a bottom date of 11/18, and we see its clear the Cayman XT has 1920 SP's... it's most likely the specs were only revealed on the 18th's conference meant for the 6900's