Just few mins back I found this website: http://www.zubrag.com/ It is PR 6. When I search for its backlinks in Google I see that it has BL from pages that are of just PR 2 or 3. But when I search for its BL in yahoo I see that it has BL from pages that are PR 5 or 6. Now we all know Google takes into account only Dofollow links while Yahoo considers both DF & NF links. It really puts me in a tizzy..or else correct me if my observation above is wrong.
Google traditionally only shows a sample of the links that they count for a site. They give credit for more than what they show with the link:www.domain.com command. I suspect this particular website also had higher PR links in the past that they stopped paying for.
I agree with vansterdam I think this site probably lost some high quality backlinks, it's pr will probably decrease in the near future.