A hacker has breached the PS3 security. The games like COD4, WaW and MW2 are filled with mods. The games are extremely modded now. Activision claims that "The mods are unfixable". Black Ops should still be fine, because it has new features that make it much harder to mod. Activision will not fix these games, so Black Ops is the only playable CoD game on PS3.
So basically, Black Ops is the only game that can be played without Excessive Mods on PS3. Activision plans to do nothing.