MaximumPC (whose name implies some bias) attributes the overheating and failure of Macs to sloppy assembly -- specifically the overuse of thermal compound on the CPU heat sinks. They gave examples of two systems in their possession that were cured by redoing the heat sink compound.
I haven't read maximumPC in a long time. Though the overheating issues with macs is the newer macintelosh line, not the "older" powermac line.
AFAIK.
But it does show a trend of sloppiness on their part.