I'd say misprint. And also considering it's minimum 5 disc for MGS4 on xbox, along with all the apple products in game, the ingame ps3 remote along with the PS3 on the nomad, I doubt Microsoft would want any of that.
This. The fact that xbox uses DVD format and not blu-ray would mean no matter what it would take about 5 discs.
That's one of the main reasons MGS4 is safe to stay exclusive is the file size. Come next gen. that could change and Konami might try to port it. Right now there isn't a console out there capable of handing the port.
You're forgetting about redundant data, it would take atleast 5 discs though it could potentially take as much as 10.