While they both work together, the domain name and the web hosting service are two different things and can each function in different ways.
However, without a domain name there would be no way to access or lead to the information stored in your hosting account. Therefore, the hosting couldn't function.
Domain names, however, can be purchased without web hosting. These domains are considered 'Parked' until such time as their name servers are delegated (or pointed) to a webhost. Advanced DNS records of the domain can also be used to point to other servers, although the IP address must be known. It may also be redirected to another domain name. For example www.mydomain.com and www.mydomain.com.au are both individual domains but one may be redirected to the other. In this case, web hosting only needs to be established on the target domain.
What is most important when considering the purchase of web hosting or registering a domain name is ensuring the quality of service. Accredited with the Australian Domain Name Administrator (auDA), and providing 24-hour technical support, service and quality is at the heart of Netregistry's philosophy.