QUOTE
The Grand Prix of Houston announced today that the 2008 event, originally scheduled for April 25-27 at Reliant Park, has been cancelled. Grand Prix officials made the determination that after the unexpected unification of the Champ Car World Series and Indy Racing League and the resulting exclusion of Houston from the schedule, it was not possible to stage the event in 2008. However, Grand Prix officials are already in discussions about the possibility of holding the Grand Prix of Houston in 2009 with the American Le Mans Series and Indy Racing League.
So the Champ Car-IRL thing has a bit of a ripple effect. It's just a temporary thing but it's interesting to see how inner-related these sports can be.