Few things, Strubes. With Square really trying to patch up relations with Sony, there is somewhat of a chance. Plus, all the problems they had with FFXIII, either they've figured them out(probably the case), or they're just not used to it yet, so they don't want to spend all that money making KH3 for the PS3(even though it would sell very high). Also, the first two appeared on the PS2, the weakest console last gen. I'm not saying there's a pattern there, just that if the first two can be that amazing, then the Wii can have a great one, as well. To reiterate, not saying the Wii will for sure get it, just saying that it could.
If we're lucky.