So according to the game's xbox.com page, Namco Bandai's fourth installment fighter isn't going to be playable for those arcade pack owners out there. While Microsoft's doctrine that your SKU wouldn't matter when it came to the simple act of playing games has been broken before (FFXI, etc) we really didn't expect to see it in a fighting game.
It could be that the HDD requirement refers to the game's Create-A-Soul mode (which would obviously require space to save created players). But has the game really been created in such a way that doesn't simply disable that feature for a user without a hard drive? The xbox.com page could be a mistake of course, because to have to leave a certain section of the potential player base (however small) unable to purchase your game just seems a bit strange. As much as this is worth complaining about, let's hope that the game uses the 360 HDD's reserved 6GB of caching space so as to avoid the mandatory install of the PS3 version (which seems to be the most likely situation, considering the PS3 HDD install is just about the same size as the 360's reserved cache.)