The PowerPC ISA (Instruction Set Architecture) is designed with different implementations in mind (a typical IBM trait if you look back their mainframe processor designs in the 70s).
You can get increadibly simple PowerPC implementations aimed at embedded systems (e.g., the PPC405, which just has a single, 32 bit, integer execution unit, and as part of the Xilinx Virtex II Pro clocks up to 300 MHz), then you can get the IBM POWER4 high end compute-tastic jobs which consume enough power that were you to try put one of those in a mac it would melt the case (according to one IBM engineer on comp.arch).
Thus, it is fair to compare the small scale, embedded minded PowerPC implementations, but obviously it makes no sense to compare the PPC970 (aka G5) with an ARM part.
The key distinction is that the PowerPC ISA was designed to be scalable from the low and to the high end, just as it was designed to support both 32 bit and 64 bit implementations. In terms of processor design it's quite unusual in that it demonstrates foresight on behalf of the original design team
I can't remember who designed what in AIM, but I can recommend Jim Carlton's book "Apple - The inside story of intrigue, egomania, and business blunders", which will probably explain it. It's facinating look at how Apple got from it's founding stages to where Jobs was brought back in. It's amazing that they ever survived given how many golden eggs they just passed up.
I'm told, and I can't confirm this, that PowerPC is generally the embedded processor of choice in mobile phone base stations.