I see that too but that I just remember that I only want three kids. That's all we can financially handle now and we live in an apartment. Even if I had a third boy and was garaunteed a girl for the 4th I still don't know if I'd go for it. I think everyone knows the perfect family size for them no matter what the gender.
My in-laws' friends had three girls and decided to just try one more time for a boy. They got another girl so I guess it's not a guarantee.