Leonard0 - 11:00 pm on Aug 2, 2012 (gmt 0)
Unmatched Ad Requests are also generated by AdLinks
Adsense Help [support.google.com...]
If you're using link units on your site, unmatched ad requests might be higher than expected. This is due to the way we count a matched ad request for link units. A matched ad request for a link unit is only counted if the user clicks on a term in the link unit.
Unauthorized sites seem to generate them too, even though the Coverage shown for the site is 100%.