I wonder if anyone could enlighten us as to the reason for the difference here. I have noticed on some Windows updates that this is also the case. Does the PPC chipset interact with the OS differently than Intel? I know that there is a Hardware Abstraction Layer in Windows that separates much of the OS from the hardware, and I'm assuming that something similar is going on with the Intel version of the MacOS.
I also know that files may be in use when a system update is applied, so they must be copied in during startup after a rudimentary kernel is loaded up. If it is a large update, this can obviously take some time. On Intel machines, has this kernel also had to be updated, thereby requiring the second reboot?
And just for the record, I installed the update fine on both my iMac G5 and my PowerBook G4, without touching permissions. (As someone else mentioned, I thought they had fixed that problem/requirement, so I don't do it anymore) Thanks to FiOS, it downloaded nice and FAST.