The report claims that Rock Band was "the number one title across all platforms in North America for calendar 2008." The key phrase there is "across all platforms" -- meaning "among games released on all three console platforms." It didn't make NPD's top 10 best-selling games.
EA's best-selling title of 2008 overall was FIFA 09, which sold 7.8 million copies in 2008. This estimate puts FIFA above three of the games on the combined Enterbrain/NPD/Chart-Track sales list.