I suspect that received wisdom is highly culturally dependent. The received wisdom in my social circle (western US) is that girls are far more trouble than boys.

What is common in the public at large is not necessarily what is common in the subculture of old money families. Still, I am not necessarily claiming that this is happening, but it certainly seems more plausible than having some psycho-somatic path where wealthier women would give birth to more male offspring. Another even more plausible explanation is that the effect simply does not exist, that the data was not properly collected.

I think a more likely factor would be stopping after the first child if it's what you wanted, and trying for more if you really wanted the other.

But there's so many other confounding factors (e.g. do billionaire men have more testosterone, as either a cause or an effect of their success, do they have children when they are older but the mothers are younger and so on) that it offers no evidence on its own.

Thinking more about my own comment, perhaps researchers expecting to find more male offspring while googling find male offspring more often!

Worth bearing in mind that the birth ratio is generally tilted towards boys, about 52.5%