"Hello World" programs are often the first thing that many programmers and scripters make when learning a new programing language. It may also be the most appropriate place to start when creating ones first blog or for that matter their first post on any socially interactive medium.
The "hello" portion is appropriate because it is one way of breaking the social ice and is also a salutation. It is also often the first word we learn in a new spoken language.
The "world" portion is equally appropriate as this blog is being published to the World Wide Web.
And finally a "Hello World" greeting is so much more friendly than a "testing, this is my first post"
Until next time,
Bye Bye World