Why use semantic markup with a CSS framework? It makes your CSS increase linearly with your content.
I'm using SASS and the Foundation grid mixins to define visual components of the site (eg tag, display-picture, etc) that can be put on any page and have different sub classes (eg tag-small, display-picture-large).
With this, the goal is not to have CSS increase linearly with the number of pages/content because I've defined all the visual components of the site and they can be shared across pages.