According to this, Bourne Conspiracy's lead game designer, Rory McGuire, thinks all Xbox 360s should have been sold with proper storage space.
I think that was one of the mistakes that Microsoft made with the 360," he said.
He added, :They did it with the original Xbox. I'm not sure why they decided to not require a hard drive on the 360. From what I understand they don't move many [Core/Arcade] units. Developers certainly benefit [from a hard drive]. If you have a hard drive, the whole game loads faster. Obviously you'll be facing a short install time, but the developer benefits from it and you definitely benefit from it as a player."
Bourne Conspiracy is out later this year for PS3 and 360.