no. We don't need so many. I think they are an excuse for people not to learn a technique themselves. In general the win from using one of these frameworks is small and the overhead is high - you'd be as well off to just learn how to lay out a grid and deal with margins/padding, etc manually. Their use also seems to come at the expense of messing up your html by shooting it with the class/id shotgun - something some people seem ok with but I dislike.
Maybe it's a sign that css needs to refined in some areas to make it easier or clearer to do the things people are try to do.