The operative word here is “guaranteed”. I agree that in most tournaments, the Winning Alliance Captain will be granted an invitation to the World Championships. That does not appear to be the case for “all” championship tournaments.
They’ve even updated the web site to reflect this.
http://www.usfirst.org/roboticsprogr...ldChampionship
Which teams will advance to the World Championship?
The Inspire Award winner from each Championship Tournament will receive an automatic invitation to the World Championship.
Most Championship Tournaments also advance the Captain team from the Winning Alliance.