Some times people register all other extensions even for ordinary domains in order to protect their website, at other times domainers effect each others actions, for example you register an average domain because you see all other extensions are taken, then after a year you realize that it was not a very good domain and you decide to drop it, next another domainer notices that domain again and decides to register it because other extensions are taken, the cycle keeps going on as different domainers keep dropping the same domain in different extensions and other domainers keep registering them because at any given time only one of the extensions might show to be available. It seems that the real good generic domains are also taken in most of the major TLDs in addition to the usual extensions , if you do a search for www.domainname (without spaces) it might show some of those extensions. You can add -.ext to your search if the results are overwhelmed by one ext. , for example do a search for ( www.book -.com ) or ( www.car -.com ) to see the scope of those domains in different extensions. IMO