A 3rd-party publisher will publish for as large an audience as it can, on as small a budget as it can, in every case, unless they're paid not to. They clearly have an engine which runs on the PC, PS3, and 360 (or they wouldn't have announced it as a port for their flagship, FF13). Obviously they have some Wii experience as well -- and it would be a piece of cake to downport a PC engine to the Wii.
The KH series has always had a simplistic art style compared to the rest of Square-Enix's projects. Its probably an easy downport, and in support of the triple-release idea, SE has a working PS360 engine already.
It'll hit all three, almost without question as I see it, unless one of the console makers is willing to fork out some exclusivity $$ to both SE *and* Disney. Disney isn't going to be pushed around by any paltry sum, either -- and that supports the "all three" outlook heavily, IMO. Compared even to MS, Disney is a monster.












