Oh I don't know if it's never, it's just longer than 2 years, and yes, it's mostly because of other reasons not entirely known, though I remember reading something about sometimes that is with people who have multiple strains.
You can usually assume you've cleared it in 2 years unless you've had symptoms or positive HPV test (done in females).
Thanks, auntijessi. This is something that I wish the HPV literature would elaborate on more. From my reading, I've been under the impression that some people *never* clear the infection.
If you haven't, check out www.ashastd.org for some great info on it, and other STDs.