From what I've seen, they can all interact with your PC and Mac universally (though my experience with the Mac "Portal of Power" has only been okay, requiring reinstalls of the driver). The actual "Portal of Power" bases, however, do look different.
The Wii version of the "Portal of Power" uses wireless USB. The 360 version has a long USB cord.
While I haven't tried one in the other, they certainly look different. The only reason I'm posting this is because I was gifted a Wii version, but wanted the 360 version and needed to find out if I could simply swap while obtaining the game disc only... not that that item is on sale at the moment.
Review to come shortly!
Related Link: Skylander's Spyro's Adventure Starter Pack