In the U.S. they used that term with at least three of our sports: The NBA,the NFL, and Major League Baseball.Their series is even called the World Series. I think it is because in these three leagues they have a compilation of the best skilled athletes in the world. This is primarily due to 1.
This is further evidenced by the fact that playing in MLB, NFL, NBA, or NHL is the goal of the world's athletes.
In baseball, everybody wants to be in MLB, and they go elsewhere after their skills erode and they want to keep playing or earn their way back to MLB.
In basketball, Tony Kukoc was his country's best player, but he couldn't even start for the Bulls.
In football, the only Americans who go to Canada to play are the ones that didn't get drafted or retained by an NFL team, or who were problem children down here, so much so that their talent couldn't even keep them on the squad.