You're right, Doubtless. Most polyandry consists of a woman marrying either 1) a set of brothers, or 2) a set of men who are particularly close. It does not involve women as simply sluts. Promiscuity and organized polyandry have the same genetic effect, though.
Human sexual behavior is incredibly diverse. The only universal is the incest taboo.
Then there's this line that bugged me: "If two out of ten blacks have smaller penises than the average white one, but the other eight have larger penises, then who has bigger dicks?" In reality, it's more like "If forty-nine out of a hundred blacks have smaller penises than the average white one, but the other fifty-one have larger penises..." Either way, it's fallacious to assume that the entire group has bigger dicks just because they average bigger. And sampling can be biased: A survey of the NBA revealed the average Chinese man to be 7'5".