Most smaller companies pay someone.
The history of How Stuff Works is typical. Twice a day, the COM, ORG, NET, etc. name servers get updates with the newest IP address information. We set up a hosting account with Tabnet and Tabnet ran the DNS for How Stuff Works as well as the machine that hosted How Stuff Works' web pages. This type of machine is called a virtual web hosting machine and is capable of hosting multiple domains simultaneously. 500 or so different domains all shared the same processor.