Looks like your a PS3 fan boy then... so your both as bad as each other
The fact they say MGS 4 takes up an entire BluRay disc is due to compression. From what I heard, they didn't use any, or not much at all.
Consider that if it ever did come on Xbox 360 (which I doubt), the textures/videos would be somewhat more compressed than on the Blu-Ray counterpart.
Think in the lines of GTA 4 on both consoles having the same content and looking pretty much the same, even though I'm sure the PS3 version again, uses up most of the Blu-Ray disc.
If it was released on the Xbox 360, I'm sure they could get it down to 2 discs easy.
Haha, if thats actually in the game though, it is pretty funny that they'd include something like that.