This article titled, “Joomla And WordPress: A Matter Of Mental Models” from Smashing Magazine contends that your choice of CMS depends on how you expect Web applications to allow for theming and core manipulation.
Open-source content management systems (CMS) are a large family of Web applications, but if we’re looking for stability, performance and average technical requirements, we’ll come up with a handful of options. In the past, choosing the “right” CMS was a matter of the project’s requirements, but now this is not completely valid because the paradigm of extensibility had driven the development of major CMS’ towards a model of core features that are extensible with plug-ins that fill virtually any requirement.
Picking the right CMS is then a matter of “mental models”: choosing the one that best fits our vision of how a Web application should work and what it should provide to users and administrators.
It’s an interesting read. I wish they would have thought about Drupal in this equation (which I’ve now come to prefer over Joomla) but the article and as usual with Smashing Magazine the comments are well worth taking a look at.