Many people have this question where they need to understand the concept of dedicated hosting and managed dedicated hosting.
A dedicated server is a server that is leased or purchased by a client. Unlike shared hosting, it will be only the owner of that server who will host websites on that server. That is, that server wont be shared with any other clients, except the websites hosted by the owner of that server.
Most web hosting companies offer 100% root / Administrator access to the dedicated server or VPS servers, i.e the owner of the server will be able to access the dedicated server with root privilages.
Now, its upto the client that they purchase managed services while trying to signup with web hosting company or manage the server on their own. Managing the server includes various tasks such as initial server setup, server security including firewall and anti-bruteforce application installation, OS optimization, application optimization, service monitoring, 3rd party application installations etc.
If the client himself has good technical knowldge of managing a server, he can just purchase the server without managed services. Such a server is called UNMANAGED dedicated server.
If the client is not sure about technical issues related to server or does not have enough time to manage his/her own server, he can either purchase managed services from his web hosting provider OR hire a 3rd party server management company who specialize in server management support.
There are various companies that offer managed and unmanaged servers such as http://www.webhost.uk.net, etc. Going with a managed server is sometimes feasible instead of managing the server on your own as in such case the web hosting company techs are more acquainted with managing the server more efficiently than a third party entity.
Most web hosting companies offer only basic server support under their MANAGED server segments, however there are few companies such as http://www.webhost.uk.net that take complete care of the server incluing server monitoring and reboot requests.