can't speak to zurb, but 960 and other 'grid' systems were just that - grid systems. I'd see "look at all the cool examples built on library X (960/whatever)", and then look and realize that it was a huge amount of customization on top of whatever base library was there to make anything look half decent.

Bootstrap looked good out of the box, and had decent styling for all major situations (including tables). 960 and other grid systems gave you just one small part, not an entire framework.