Assigning of Internet addresses is the classic example of this. With thousands of new users registering every day, no central registry could hope to keep up. Each level keeps track of the levels beneath it. Well, various registrars handle the busywork of assigning addresses, making sure there are no duplicates, etc. These firms are simply acting as agents of the Internet gods and have no authority of their own.
Many people register in all three domains to avoid spoofing by wiseguys.
Once you register your subdomain name, you become the registrar for any sub-subdomains you care to establish. The domain registrars parcel out the subdomain names, the subdomain registrars parcel out sub-subdomain names, and so on down the line. The names of the levels are separated by dots. Actually locating a particular computer on the net is also a decentralized process. An IP address is simply a number, which computers find easier to deal with than words.