I had heard that the Wii version was different, but then I was surprised to see just how different it was. Imagine the design for the gameplay was done, but then two companies actually executed it. I haven't finished the Wii game, but I haven't seen any parts of the level that are too close to the 360 version. It's much more "linear" in the sense that there are more hallways and less turning around or even side to side. I think that's to accomodate that the Wii controls didn't provide a way to turn the camera very well.

So, yeah, that plus the fact that very few games on the Wii get DLC (I assume for technical as well as financial considerations) I think that's why the Force Unleashed hasn't gotten additional content like the 360 and the PS3.