I suspect that the trailers are lying. Sylveon doesn't say its name in Pokémon-amie, so either Pikachu only says its name in the trailer (likely), Pikachu is the only Pokémon to say its name in the game (unlikely) or all Pokémon will say their names (no chance lol).
Harmony is peace. Peace is unity. Unity is harmony. I tell this to the King Nook. He ask me to leave.
Pikachu sounds good saying its name. I recently decided to watch more Pokemon anime, and was terribly disappointed when a Heatran said, 'Heeee-traaan' with a Flamethrower or whatever. It just sounds terribly bad for the majority of the Pokemon to cry their names, in my opinion.