(This post contains shameless self promotion)
I think GUI elements are an essential part of a web development framework nowadays. I maintain a small open source CMS called Enano. It's very basic, but during the course of its development I've written a ton of GUI building-blocks, among other frameworkey things, and documented the APIs for them so that plugins can use the same features. Regarding the GUI elements, I think consistent interfaces are an important part of any web application. Thus, what better way is there than to use a good, solid framework that, among its other jobs, takes care of some of the GUI design ugliness for you? Stuff like a standard way to present and validate forms, show message boxes, log in users, provide visual feedback for a process, etc.
In my opinion, a framework should do more than just provide a bunch of random pick-and-choose APIs that you can use. It should take care of the boring details you don't want to have to rewrite for a web app, like user account management, sessions, user data, database abstraction, that kind of thing. That's why people are writing applications using software like Drupal and Enano: they want to write a web app that does what it needs to do without having to reinvent the wheel. I'm currently using Enano as the foundation for an e-commerce site (contracted project). Yeah, eating my own dog food, but shows that it can be easy to take something like Enano/Drupal/Wordpress and use its existing, established core features to write a whole new application that uses those features.
Yes, I've used a more traditional framework before (CodeIgniter). It's great, and I love its design for basic applications, but you still have to write your own user management and a lot of other prerequisites to create something like an e-commerce site. In contrast, I've developed the entire e-commerce plugin with about 50-60 hours of work, including a couple of very minor modifications to the core.