The BD containing the game amounts to 38GB, whilst the Xbox 360 version has already been confirmed as being packed onto 3 DVD discs (offering an absolute maximum of 25GB or so).
Add to this the fact that each disc will have to duplicate key game resources and the amount of space available to the Xbox 360 version drops even further…
However, concerns over a crippled Xbox 360 version are misplaced – of the 38GB of data on the disc, only 8GB is game data, the rest being given over to sumptuous CG movies (see above), leading to the promise that the in-game elements will be “mostly” identical, whilst the movies simply enjoy far lower data rates to compensate, an admittedly dubious consolation.