A previous report of a PowerBook G5 reference sparked a considerable amount of speculation amongst Apple fans last week.
Another Apple website reference was submitted at http://www.apple.com/ca/fr/displays/asd17/ (in French). The 17" Apple Studio Display info page lists the following under configuration requirements:
LApple Studio Display ncessite un PowerMacG5 avec un connecteur ADC ou un PowerBook G5 avec un port DVI vers ADC Apple ; Mac OS X v10.1.3 ou Mac OS 9.2.2 ou ultrieur requis.
The previous reference was to the Power Mac G4 and PowerBook G4 in Feb 15, 2004 (Web Archive), so may simply represent some overzealous editing.
Update: Corrected at Apple site.