The reason WordPress has NOT been taken seriously as a full-fledged CMS is that, for most of its life, WordPress has not allowed you to create complex content t

The reason WordPress has NOT been taken seriously as a full-fledged CMS is that, for most of its life, WordPress has not allowed you to create complex content types. You were pretty much limited to "blog post" and "page" types. Sure, you could create your own basic type that was essentially a copy of the "page" type with another name, but the only fields you could add to that type were WordPress's "custom fields" -- which acted more like unstructured metadata fields than true content type fields. I understand that this has changed somewhat in WordPress 3.0. (I have not had the chance to try it out and verify.) But it's a bit late -- Drupal, Joomla, and Plone have gained much more traction as full-fledged CMSes in the intervening years.