Lately we've been seeing more and more games for the PS3 require a hard drive installation to play. It's become such commonplace now that no one is really making a big deal out of it. Honestly, it's not such a big deal for PS3 owners because they can install a large hard drive on the cheap. Xbox 360 owners, on the other hand, aren't so lucky. Which is probably why there will be a large number of people upset by Soul Valibur IV.
According to the official Xbox 360 listing for the game, you will be required to have a hard drive installed on your system. We don't know exactly how much space it will require, but with most people only having 20GB drives (if they have one at all), I certainly hope it will be a small installation.
As for those with Core or Arcade systems, it looks like you'll need to shell out the extra dough for an over-priced hard drive. Perhaps one day Microsoft will actually lower the price of their hard drives, or let us install our own. I'm sure that'll happen around the same time Duke Nukem Forever hits stores.