I'd guess the average was based upon a very high grade coin... Click on the price and you'll see the specific auctions and grade. [edited to add: I was right, they were both PR 70s: http://www.pcgs.com/AuctionPrices/details.aspx?s=93488&c=45&sr=0 ]
It is for one of their collectors coins. High end "condition rarities" they only slab so many to keep up demand. How else does a $2 (for example) MS-68 become a $2,000 MS-69? For the collector who just has to have the best. (And doesn't know better.)