I find that obnoxious too. Particularly in the pregnancy books, where they make it sound like your own fault your baby's neural tube failed to close. Some women simply don't process folic acid correctly and need a LOT more. I refuse to be blamed for a biological error in my genetic coding.
Folic acid helps the ovum mature.
In addition to helping the neural tube close, the folic acid does something as the egg is maturing to make sure the woman doesn't ovulate before the egg is really ready. I read an article by a nutritionist that stated that the majority of cases of Down's syndrome, for example, are caused prior to ovulation because the egg isn't really ready to be released. Some of those methods result in surprise pregnancies more frequently. It's also known that the Pill reduces a woman's ability to process folic acid. That same article likened high doses of folic acid, in the 4 miligram range, to the polio vaccine.