suppose someone is trying to go to
www.google.com and he mistypes the
url as
www.hoogle.com or
www.zwoogle.com or whatever. then if such a
site exists he reaches a site on which he had no interest and thereby
creating invalid ad impression or click( if adsense ads are shown
there). so inorder to protect the interests of advertisers adsense
publishers are not allowed to have domain names like that.