Yeah that sucked when I heard about it for the Japanese game! I wish Kingdom Hearts trailers would stop showing scenes that will never happen in their trailers!
(facepalm) The cutscenes ARE in the game as apparently you weren't listening. -_- They're just relocated and modified.
Consider this trailer like a "beta" trailer. I mean, look at the battle system. That changed A LOT in the final game.
Anyway, like I said before the scenes are still in the game... but the locations are different because the locations shown in the trailers were just prototypes. Like when MX and Ven were in Olympus Coliseum, that scene is still in the final game but instead of Olympus Coliseum, it's in the Keyblade Graveyard. The areas you see in these old trailers are just prototypes. Nothing more.