Wordpress started as a simple blog content management system. It can easily be converted to present a professional looking website with static (non-blog) pages if required. I use it because many of the people I design websites for want to be able to very easily maintain the site content themselves. There are other simple content management systems out there. Most of my users are ngo’s or other not for profit organisations, so i needed a free open source solution.
You can explore various demonstrations of them at http://www.opensourcecms.com/. Click on the portals and blog cms options on the left hand side.
I chose wordpress because I had to start somewhere and I liked the way it used css, and the ease with which I could create different templates, styles and themes. This was in great contrast to a frustrating experience with typo3 which has a great range of functionality but not that easy for non-technical people to use.
Movable type has just changed it’s licensing, so I thought I’d skip that but it is well regarded. Joomla of course has also been recommended to me. Mambo was another option, a pre-cursor to Joomla. I had a quick glance at Joomla but decided to stick with wordpress for current projects.