I sure hope Nvidia comes back and doesn't end up like AMD in the CPU market. They've made some incredible cards and its kind of painful to see them hurt so bad.
Far from X86. There aren't even in the same paradigm. The power pc chips (which IBM still makes under the name POWER) are RISC (reduced instruction set) based, whereas x86 is CISC (complex instruction set). Although the lines have started to blur in recent years between RISC chips like IBMs POWER line and Intel and AMD's CISC chips, they are still distinct.
Wikipedia has a ton of literature on the topic if you want to know more.