Google only shows 3 backlinks. However, if you check how many Backlinks are under consideration you won't be amazed by there pr5.
Even google doesn't show all their links, I think their links in google webmaster tools has something to do with their PR. We never know if how many quality links does this site has.
Hersheys is right there is the webmaster tools but.. you also have to remember Internal Links are known to pass small pr.. and the site has 10,000 links indexed already..