There are many different types of websites. Certain types of websites require more maintenance than others. I'll describe two:

Static website: one that consists of individual web pages stored on a server machine in the same form as when they are transfered and viewed on the client machine (using your browser). 

Dynamic website: one that consists of scripts that pull the content from a database each time a request is made. In other words, the web page is dynamically put together by the server each time before being sent to the client machine.

Let's say you want a plain, static website that rarely, if ever, gets updated. Obviously, you don't need a maintenance contract for this particular type of website. On the other hand, if you decide to build a static website in which the content gets updated regularly, then, unless you do the updating yourself, it falls upon the webmaster to take the content you've provided and integrate it into the existing website. In this case, the decision would be whether to go with a maintenance contract, or pay on a per update basis.

With a dynamic website, the issues are different. Both Joomla! and osCommerce are dynamic web environments. You'd want to use such a website if you are updating frequently, or have products that you want to sell. The advantage is that you can do the updating yourself, because both Joomla! and osCommerce provide a web-based interface in which to modify the content of your website directly. Such websites, however, still require maintenance in the form of occasional security upgrades to prevent the system from becoming vulnerable to exploitation.

Full system upgrades can at times be complex, especially if the dynamic web environment has been highly customized.

Totalnetqc always informs its customers of available security upgrades. 

Totalnetqc offers its customers the choice of a maintenance contract or a pay per update scenario.