The PlayStation 3 and Xbox 360 versions were the only ones that featured downloadable songs.
In addition to Simon Cowell and Randy Jackson, Paula Abdul's name, voice, and likeness appear in this title for the first time. Ryan Seacrest did not return to voice himself as the host. He is replaced with a lesser known voice actor Johnny Jay to voice as the host of American Idol for this game.
The PlayStation 3 version is the only one that has all downloadable songs available on the PlayStation Network marketplace. The Xbox 360 version has six songs discontinued from the Xbox Live marketplace for undisclosed reasons. On November 18, 2008, the downloadable song "I'll Make Love To You" became available again in the Xbox Live marketplace.
Source: Wikipedia, "Karaoke Revolution", available under the CC-BY-SA License.