By your reasoning ARM is dead end also. I am sure that a eight core XEON can emulate an ARM cortex A8 or even ARM cortex A9 (even multicore)
Sure it can, but the ARM has low power consumption on its side. Both the x86 and the PPC get very power hungry as powerformance increases. The x86 has a lot of money behind it so intel/AMD improve the fabrication process to reduce power consumption... PPC doesn't have that...
