Key Xbox executive, J.Allard, has today confirmed that the Xbox 360 may not always ship with a hard drive. Developers have been warned not to rely on a hard disk always being in the Xbox 360 in their upcoming and future releases.
At present the Xbox 360"s basic specification shows that the console will ship with a hard drive, but this may change in the future. It also seems that Microsoft may ship later 360"s with HD-DVD drives as opposed to the standard DVD-Rom drives it will ship with upon launch.
Microsoft still may ship multiple specification models of the 360 on launch, one which may not include a hard drive.