None of those links say the game is Gamecube exclusive... and they don't even know wether or not it's just a port of MGS2... Although from what Miyamoto said it sounds like it's more than that, but still, not necesarily NGC exclusive.... Although it hasn't been announced for PS2
Since MGS3 is already in the works for PS2 (I think), I hope it's a remake of an older game instead of a port of MGS2 or another version of MGS3...