The Xbox 360 Version of Soul Calibur IV will require the Hard Drive for Xbox 360. This along with the huge install on the PS3 version really makes you wonder about how much optimization Namco Bandai is putting into the game. Its unfortunate for Core/Arcade owners and for 20GB PS3 owners or those reaching the limit of their HD space on both consoles...
http://www.neogaf.com/forum/showthread.php?t=323087