Then there are various other non-semantic classes: .btn, .pull-left, etc. It seems to me very much a toolkit built with a developer's mind ... in mind.
I like crafting my css by hand, making it easy to read and understand and above all - easy for me to remember so I don't have to crawl through documentation trying to remember if this element is .span4 .span-4 .span_4 or some other permutation I can't remember. I can easily remember .one.column. Its a column and its one.