Nice metaphor, but what does that have to do with anything?
Are you disputing the .15 correlation rate for dizygotic twins, and .5 correlation for monozygotic twins? That's what the reference book says.
What!? C'mon, I gave you some credit here and now you're giving me second thoughts. If you don't understand how the metaphor applies to the Bailey and Pillard sample then I've given you too much credit. They demonstrated a blatant disregard for scientific principles. First, your question incorrectly implies their study was valid and you're asking questions based on this same invalid study. Second, Bailey and Pillard would not agree with you. Do you normally accept bogus studies as relevant?
Answering this question will help me understand from where you're coming: Do you think the Kinsey study was based on valid samples? That's a very relevant question for this topic. Here's another off topic but relevant question: Is Al Gore's global warming based on sound science?