The explanation was quite pleasing. The story goes that the original sponsor of the World Series was the 'New York World' newspaper - hence the name. Nothing what-so-ever to do with someone confusing their country with the planet.
Thanks to snopes urban legend reference though I've since found this explanation isn't right at all. Unfortunately while the story is disproved no satisfactory explanation of where the name comes from is provided. Did someone really not realise that there is more than one country in the world?