The essentiality of oral sex

Via Feminist Philosophers, which is a blog that everybody ought to read, I found the following tidbit on oral sex and nature great, but I have absolutely no understanding of my reaction:

Oral sex is surprisingly rare in the animal kingdom. Humans do it, of course. As do bonobos, our close relatives. But now researchers have observed the practice for the first time in a non-primate. During intercourse, female short-nosed fruit bats lick the genitals of their partner, a possible ploy to increase copulation time. The discovery suggests there may be a biological advantage to fellatio.