Word Count

Tweets can be only 140 characters. A blog post can be any length. Is it ethical to have a blog post shorter than a tweet? Or does it cheat the reader? Is it a sign of laziness on the blogger's part?

Haiku are generally supposed to be seventeen syllables. (Yes, I know there are exceptions.) Can a blog post have fewer than that?

I'm used to writing for children's magazines which have strict word counts. Blogging is a whole new world...