Both which were not made by Kojima's team. Only port worth mentioning is the GC port because it was pretty good port, but the xbox port...or was the Xbox port? GC port definately wasn't.
I wouldn't put my money on MGS4 arriving to Xbox360.
Port or not both of those consoles got a MGS game despite the 60+ million PS2 install base. With PS3 struggling to gain marketshare vs X360, shareholders have the power to force certain exclusives to become non exclusive, just look at RE4 which was an exclusive that became nonexclusive due to shareholders.