I have never try Joomla. I started web design back in 2003 using dreamweaver. I dont write html but focus only on the design element and its web content. It is very limited in itself and static. I stopped doing web design for 10 years and went to do something else and came back to touch it because I want to do a personal website. Searching around, I found that word press is a good CMS as it offers alot of functionality that is free and many of its alternative. One could try out the various plugin for suitability before shelling out the dole to commit to it.
I guess the value of Word press is like what other have said, lies in it thousand of plugins. One can use it for a start and then migrate to others when the knowledge or have hit the limitation of wordpress.