Maybe it's like a race game; after you beat the game you unlock "mirror" mode as a cheap form of replay! YAY
But, look at the mini-map. Yes, the Wii version is mirrored on the Y-axis, but there's more to it than just that: rather than having the area exit be north, it now exits to the northeast. Perhaps the layout change was made to fit with the next area's entry (i.e. entry from the southwest). And, to justify the mirroring, perhaps the northeast part of the map was unaccessable under the original design, and that it was easier to mirror the small area rather than reconstruct the northern section. AND, maybe they couldn't have altered the northern part of the map even if they wanted to, due to some sort of puzzle... such as mirrors. (
, sorry)