@DennisN,
Huh, that's a historical question and a large domain registration site probably would not give you the particulars (or would charge you for them), but they might at least be willing to give you an aggregate number. It may also be considered to be something of a privacy violation if they were to give the names out (or at least a violation of their own Terms of Service/contracts with their clients), seeing as people and corporations often purchase URLs they will never use, just to keep others from using them, or to squat and see if they can get some $$ for them.
For example, someone might own SuperBowlWinner2112.com and be figuring they will pass it onto their grandchildren who will sell it as squatters. Or Widget Maker might own WidgteMakersucks.com or the like, in order to prevent disgruntled customers from using that URL to complain.