Here's the explanation from the Rock Hall itself:
Next week's edition of American Idol will feature a Rock and Roll Hall of Fame-themed show. The Museum's story and mission will be highlighted throughout the shows and the final four singers will sing songs from the Rock and Roll Hall of Fame and Museum's list of 500 Songs that Shaped Rock Music.
Rock Hall visitors can experience digital jukeboxes of all 500 songs in the Ahmet M. Ertegun Main Exhibit Hall. Five touch-screen computer kiosks with headphones allow access to some of rock's most popular and influential recordings as selected by curators, rock critics and historians. Arranged by artist and decade, the songs cover a variety of musicians and genres and are accompanied by information about the selection and its role in the evolution of rock and roll.
For a complete list of the 500 songs, click here:
I seriously doubt the singers will have all 500 songs to choose from, since that would involve a lot of rights acquisition by the show. Still, it will be interesting to hear what they end up choosing. I'm told the contestants will not be coming to Cleveland, but the Rock Hall is providing footage of the facility for use in the show.