Yes, I didn't mean that the PPC per se is dead, only its use in the kind of applications that's interesting to us. Apple were the last desktop and laptop manufacturer, and since Apple left, the whole PPC business changed focus. The future for PPC is in various embedded applications now, routers, printer servers, automotive, etc (and by all means, game consoles).
Already at this moment, ARM chips (Cortex A9) are *on par* with PPC G4 performance wise, and upcoming Cortex A15 will introduce a whole new level of performance and features, making it suitable for servers/desktops etc. And in a few years from now, nVidia will release their own ARM CPU's, what they themselves call "x86 killers", especially targeted towards high-end desktop, workstation and server markets. More manufacturers are bound to follow, that's the beauty of ARM's license based business model. And even Microsoft is on the train, and will release Windows 8 for ARM! So ARM definitely has its future ahead of it! 
NVIDIA hasn't proven themselves to be "fat" OOO CPU designers and NVIDIA has to be carefull with OOO CPU patents...
On core vs core, Cortex A9 is dual instruction issue per cycle lite OOO CPU that implements 64 bit SIMD hardware i.e. like SSE before Intel Core 2, ARM's Neon ISA is 128bits wide while the hardware is 64bits.. G4 implements 128bit SIMD hardware. The one of the main problem with old G4 is with it's slow FSB.
PS; K8 Athlon implements 128bit FADD SSE1 in hardware. AMD Bulldozer implements FMA4 which is superior to ARM/PPC's FMA3 format.
AMD Bobcat and Bulldozer cores implements pointer based register rename trick i.e. similar to Cortex A9's register renaming trick.
Note that AMD's GCN (GPU Core Next, Radeon HD 7000 series) includes AMD64/X86-64 IP i.e. AMD is building it's own X86-64 based Larrabee.