I think also the legal(licensing for music and what not) and shader precomputation.btw, people aren't talking enough about the fact that native XBox games will be able to run on PCs.
There's talk of updating the Windows API to provide native support so that XBox games will run on any PC.
This is great for those who have libraries from years ago. The only thing preventing it from running today is a slightly different API on the part of the respective operating systems, but it's purely a software issue that depends solely on adding that API to the current Windows operating system.