Could also be measurement error...

Could be, but its probably also a cultural thing. Most Americans don't view oral sex as sexual contact, and yet, most STIs are transmittable from it. This, alongside sexual education in schools that focuses on that 1% (used correctly) failure rate of condoms and lack of hard scientific evidence it will prevent the spread of HPV, leading them to think "condoms are unreliable, so why bother?" has led to a thriving youth culture of unprotected oral sex...and later, when they become sexually active, unprotected sex.

And it just so happens one of the primary ways women catch HSV-2 is through a partner infecting them orally. There are "virgins" getting herpes in America.

Now, again, culturally, I've been told that Aussie men are incredibly chauvinistic, so maybe a smaller percentage is likely to engage in oral sex. I'm generalizing and speculating here , so take it with a grain of salt. In the UK, the sex education could be better. From talks with my friends from southern states, it seems you'd have to deliberately try to do worse.

Just to add a little elucidation to the sex-ed thing, the places that don't focus on abstinence as the only technique don't really explain the numbers. That's a 1% chance that after a year of regular sexual intercourse. Which makes the per-use numbers much, much smaller.

Furthermore, there was at least some issue in that many doctors were more conservative, and didn't really like talking about oral sex. (I heard this from a doctor who was complaining about this).

I don't doubt the WHO's overall estimate; just pointing out a contrast -- both between regions and in what numbers astonish people.