That's interesting that its close to an even split. I have the same curiosity as you - is our desire for a particular gender linked to our own gender the driving force, or are particular people (and I don't mean that in any way to be a judgmental thing about a person's character) prone to just wanting each while others are happy with the same of whatever ITMS.
I can't speak for men everywhere, but I am confident in saying that my DH couldn't be happier with his brood of girls. He is not a bloke's bloke by a very, very long way but he is incredibly sporty. It is something we have talked about quite a bit and he has always consistently maintained that he has no disappointment whatsoever at not having a boy. His dad on the other hand, not so happy about our inability to produce someone to carry on the family name!!