Yes, there are generally slightly more boys born than girls. This is probably explained by the fact that male sperm swims faster than female sperm. Female sperm travels slower, but is more hardy, so you're more likely to have a girl if you have intercourse a while before ovulation, and the sperm has to hang about, iyswim.
Ok, the sociobiological explanation is a bit complicated, and mostly based on what I've read in Hrdy. Basically, there's evidence that other primates do sex selection for their own advantage. For example, in a primate species which is matrilinial/matrilocal (girls stay in the troop they're born to, and if your mum is important in the troop, you probably will be too), the top women mostly have girls, to carry on their empire. The bottom women have boys, who will generally move to another troop, and have a fresh start, anyway.
For primate species that are patrilinial/patrilocal, top women have boys, bottom women have girls.
So primates definately have the capacity for status-based sex selection.
Humans are generally patrilinial. Also, historically, if you were well-off and in good health, and likely to produce a really smart strong and healthy child, you'd be better off having a boy. Because historically, women generally all had about the same number of kids (somewhere between 0 and 10, I'd say), but the bulk of men would have 0, and a small number would have hundreds or even thousands (think emperors with harems etc etc. Or Wilt Chamberlain, in the modern day). So if your body thinks you're in a great position, likely to have a great kid, a boy is a good idea. Otherwise, better to play it safe, and have a girl.
I have this theory partly because I live in a socially mixed area - lots of working class people, lots of middle class people. Almost all the local mums I know are middle-class, and almost all the local mums I know have boys. But then, most of us feel quite rich and priviledged, because, compared to our neighbours, we are.
So there, you asked for a real blurb on it, you got it.
I suspect that intercourse timing and dietary changes which hopefully will affect the mucous are more likely to bring you the desired gender of baby than convincing yourself you're poor.