It was a minor error, that thankfully Atlus didn't catch, they would've probably delayed it even more. Or they did catch it, but didn't want to delay the game any further or fans would riot on the streets.
Even though they never really explained why the evoker was necessary in the games and left the interpretation of it to the players, it was really stylish and does help the Persona series stand out a bit from the millions of other monster summoning RPGs.
Tony, for some reason the trailer download doesn't work for me at all, when I tried playing it with Windows Media Player, it wanted me to download a license thing. Doesn't work with Zplayer or VLC player either...