I think that KH is a rather large game, so it would require two game cartridges.
And 358/2 Days probably won't come out on the PS2, as it doesn't have the dual-screen capability, and (if square enix employs it) the touch screen.
Also, fun fact: Square Enix solely used to be on the Nintendo platform, but it moved off to Sony consoles. But now it's slowly coming back to Nintendo, what with games such as The World Ends With You and the Final Fantasy games, like Crystal Chronicals, or Chocobo Tales.