I hadn’t heard of DRY before, but it was one of my goals when creating the open source OOCSS library. http://wiki.github.com/stubbornella/oocss/
To me, it just makes sense that you make reusable visual LEGO. Depending on coding style, meta-frameworks can make this harder to achieve. Philosophically, SASS tries to avoid multiple class names, which are one of the main methods for achieving truly DRY objects.
There should be very little difference between these four sites in the CSS. My guess is that they would share 90-95% of the CSS and 100% of the HTML.