Hi Ray,
It looks like Augray already explained this to you. The Lewontin paragraph you quoted was followed by a paragraph that begins, "The trouble with this analysis is..." That paragraph explains why the analysis presented in your quote doesn't hold up.
I think there must be some more global context that we're missing, because Lewontin's eventual point seems both dumb and poorly made, and Lewontin was neither dumb nor a poor logician. But I can't even guess what that global context might be.
--Percy