Um, what? For all practical purposes, those apps you mentioned are frameworks. Joomla actually has a pretty firm MVC structure inside, and IIRC Wordpress's codebase has a rep for being hard to work with. Drupal makes no bones about being a framework. These are not good examples to support a "just stick it together" philosophy, if that is indeed your philosophy.

You have to stick the layers together at some point, but you'll still probably be better off keeping the glue out of your "business logic".