Because they're trite. For example, it seems like whenever somebody posts an article about databases, there's a comment saying, "Whoops, looks like your databas

Because they're trite. For example, it seems like whenever somebody posts an article about databases, there's a comment saying, "Whoops, looks like your database doesn't scale after all! Haha". Similar versions (such as this) for web hosting, etc. If you're going to take the time to post a "hey is this down" comment, at least link to the site's google cache or something. Otherwise it's just noise.