I'm excited. No, really, I am!
However, by putting it on the Wii, it'd help establish it in the console race. I'm not going to go all Square-Enix fanboyish here, but while Square-Enix's name still has some value, it would do a lot more for the Wii than for the already-successful DS.
But, they're in it for the money, it's not their duty to sell new consoles, and DQ IX would certainly bring them the money they want. Or lots more of it, anyway. Hopefully that'll make them and Nintendo more chummy on fronts other than handhelds.
Won't this game be confused with Dragon Quest Monsters: Joker? At least for the uninformed in DQ matters.