"It's simple and easy to use by the end user, but try being a developer with WordPress"
We're going to have to disagree on this point. I have been developing on WP for a number of years and continue to prefer it as a platform. Many of the projects were applications outside of the the blogging realm, including: inventory management, shopping carts, geolocation mapping, and emergency alert systems.
Though, as you noted, it's best feature is how easy it is to use for the client. Overhead for training and support has always been less than with other CMS options.