All that is being discovered is that sons mean more grandchildren, and a few groups (billionaires, top-ranking wives) are cherry-picked because they have more sons. Dung flies are mentioned but they are not even mammals, and they aren't sex selecting their sperm.

That said, though the article claims a mechanism is unknown, diet can influence whether a girl or boy is conceived:

http://genderdreaming.com/2011/05/the-french-gender-diet/

http://www.rbmojournal.com/article/S1472-6483(10)00549-3/abs...

My own wild guess is that the observed diet factors, or at least certain states of the body that diet can cause, account for any statistically significant distributions of sex, not a mysterious sperm-guiding mechanism.