Actually, they are not hyphens; they're dashes.
Dashes are often used in informal styles. They often set off material which is secondary in importance. They can also show where a short pause might be taken in speech, or where the author's thinking has suddenly taken a turn toward a different but related idea. In many cases, the text could have been written without the dashes, commas being sufficient.
"The 2004 Miss World is about to be chosen" is completely fine standing alone, by the way. It's a complete, grammatical sentence.