It was actually confirmed before the game even came out that moves like Refrigerate would boost power in addition to changing the type. I guess people just forgot, or assumed it was talking about STAB.
Anyway, I don't meatgem, but is Sylveon able to learn Nature Power? It seems like the kind of Pokemon that could, and it becomes Tri-Attack in online battles. Fairy type STAB Tri Attack with +30% power would be... nice. I know at least Mega Gardevoir can use it.
Although that would be really cool, Sylveon can't learn Nature Power, at least not through TM.