Why do some games on the 360 Have Black bars at the top and bottom?

Lost planet, Ridge Racer 6, DBZ burst limit, Burnout paradise, Forza, Pure, Soul Caliber 4, all have black bars at the top and bottom something like when I play dvd's, but not the games I own like NBA 2k9, COD2, The Orange box is that HD? I have my HD cable set on normal using component cables at 480i on an sdtv.....