yes, the reason is that when the site is slow, which happens every now and then, the preview function makes it even more annoying and slow to post a comment.

I don´t think it serves to any purpose. I never bother to re-read what I type and and roll down to press submit as quickly as possible... I don´t think that the preview function will stop some people from posting BS at times....I wonder how many members "really" preview their comments before posting?