[giulianob]

Exactly. I think web devs want to believe that their HTML is purely content and CSS should fully drive appearance but that's never the case. It makes sense to create classes when you can come up with patterns and want to make sure that you aren't repeating yourself everywhere but simply moving the grid system into CSS just adds an extra layer of abstraction that makes it more difficult to read. Also, CSS doesn't support mixins (yet) so you end up with a lot more generated CSS than if you just use the classes.