A short story (to paraphrase Stephen King) is like a kiss in the dark: short, sweet, and if it doesn't work out, you can move on without regret.
"World's Shortest Stories" is like that, Its 55-word short stories lets you try, linger if you enjoy, otherwise move on. In the end, you have a better idea why one story works for you and another doesn't.
Working within a 55-word limit can impose an economy of style that serves the reader well. This applies to blogging as well as to fiction; today's readers have a heck of a lot to read, and wasting their time is bad. In addition, writing can easily fail where the author feels the need to hit a certain minimum before publishing; I know that I don't write as often as I might because I'm too busy twittering, or facebooking, or otherwise putting down short thoughts that don't rise to the imagined minimum required for a blog post.
So the heck with minimum length. If 55 well-chosen words suffice for a short story, why not for a blog post? Let's see if I can write 55 good words a day!