Except that both Universal and SeaWorld are suffering the same economic problems, layoffs, hours cuts, job loss that Disney is. And even if Disney announced tomorrow that they were building a new themed coaster, it would be two years before it came online. So it's not like that will help today. All that would do is cause people to say, "Well ... we were going to go to WDW next year, but let's wait until Roller Coaster XYZ comes on line a year later." Not exactly helping.
Parks like SeaWorld and Universal are finishing projects that were announced years ago and have nothing else on the books. It's simply luck of the draw that they just happen to be building / opening new coasters this year. It's not like the head of AB/InBev looked into their crystal ball three years ago and said, "You know ... in 2008/09 there's going to be a financial crisis, so let's start building a new coaster now so that we have something new that year!" Hindsight is 20/20.
Believe it or not, American Idol IS bringing people into the parks. I know the AI critics don't like to hear it, but people who would have never come to the studios are going there to audition, watch or support their friends. It's doing just as well as any other new show attraction ... better than some.