Wordpress is great for many different types of websites, especially for novices who need something simple and easy to setup and use. It is great for blogs, which are it's original application, but it can also be setup for ecommerce websites quite easily using just some plugins and/or themes.
Wordpress has so many more uses than what it was originally created for, so it can be used for many different types of websites and the types that it is used for is growing all the time.
Because of the versatility of Wordpress I don't see anything taking over it's spot as the top CMS in the world!
Cheers, Dean.