An i7 is also a 4c/8t CPU. To my knowledge, the FX series are shown as 4c/8t CPUs because they need to be handled in the same way a hyperthreaded Intel CPU is handled. Because the cores in an FX share resources, you don't want to load up both cores in a module if there are other cores free, much like you don't want to load up both threads in an i7's core when there are still other cores free. Loading up both cores in a module will result in a pretty bad performance penalty, because FX cores share something like 70% of their resources and are not "complete" cores on their own.