From the AppleCare Knowledge Base:
This software updates Mac OS X 10.2.6 or 10.2.7 to version 10.2.8.
Important: This update works only with Power Mac G3- and G4-based desktop and portable computers, including iMac, eMac, and iBook. This update does not work with Power Mac G5 computers.
Given that 10.2.7 is exclusive to G5 systems, why (pray tell) would you tell us that the 10.2.8 updater will update 10.2.7… but won’t work with G5’s? Boy, I love tech support staff.