I don't think long post should be measured specifically in word count. Your post can be 400 words and be too long because it's a goddamn chore to get through and your post can be 5,000 words and not long enough. Word count means less outside of a written assignment in school. If your post is 1,000 words and 600 of those words are about putting on a sock then your post is too long. 

Also, fluff isn't a four letter word. Purple prose is what people want to avoid because then you're George R. R. Martin talking about butter glazed hams for ten pages.