I wouldn't say it's definate that it'll be on Xbox 360 but it is extremely likely.
Microsoft are doing the same kinda thing for Halo 2 on PC. You can't play Halo 2 on a PC unless you have Windows Vista.
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Halo 2, the game that redefined first-person combat and multiplayer action for millions of gamers worldwide, is set to explode onto PCs exclusively for Windows® Vista
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The whole article can be found
here.