It's all about manufacturing
Apple generally only changes the material shipped with equipment unless they'res an OS upgrade or somehting of the like. iPhoto was released the same day as the iMac. Adding iPhoto to the basic system install does take alot of work-so in order to keep products shipping...they include the CD in the box. Even now, most people that get iPhoto preloaded on their machine stilll have to upgrade to iPhoto 1.1.1.
Their is a lag in shipping all hardware from Apple now as they hold product at their warehouse-not to preload Jaguar, but to throw the update CD's in the box; at least for the current models like the iBooks, PowerBooks, eMacs, and iMacs.
It'll be probably mid to late Spetember before they change over the machines's restore CD packs to inlcude Jaguar.