These days, most sites - especially the complex ones - run on what is called CMS (Content Management System). It may be Joomla, WordPress, Drupal, or any other less known system, but those sites work by extracting information from a database and displaying it through a design, called template.
HTML sites, on the other hand, rely on information included in EACH page. In other words, each page is uniquely designed. With substantially less coding, these sites are perfect for those who need speed, reliability and a small presence on the web.