I was really just responding to the point that you should "ask any school child" about China's nuclear capabilities.
And really, nobody is going to know everything about everything. Obama basically admitted that he didn't know a crap load of stuff and said he'd rely on advisors and experts to help inform him as president and that seemed to be okay. The fact that a higher standard would be placed on one candidate than was placed on another is...irritating. Foreign policy can be supplemented by bringing in former ambassadors, speaking with former SecsofState, bringing in other qualified experts, etc. If it's worked for other presidents (surely Obama was not the only one who relied on help from others with more knowledge than he) it can work for the next president(s).
I liken it to Obama's stance on GITMO. He was fixated on closing it down, determined to end its use as an indefinite holding cell for uncharged enemy combatants. He even signed an EO with a precise date for closure. But GITMO didn't close and little was done with many of the ECs being held there. After learning how challenging it would be to find states willing to house these prisoners during and after trial, and after learning the exact details of GITMO's use, the plan changed. Would people say he didn't know enough to be president because he made an uninformed statement about GITMO's practical use? Would people say that he should have known and understood everything about GITMO before he became president? Probably only the hacks, if anybody at all.
So Herman Cain was wrong or distorted regarding China. Now he knows, and hopefully he'll take steps to learn more. If he doesn't, I'll be concerned about his capabilities, but my immediate reaction isn't to label him defective and incapable. You can't possibly know everything, and sometimes you just plain blank on information.