It looks as if Piggy has had a necklace of some kind added to her, her arms have been spaced further, and possibly a face change. The problem with yellow hair is that it changes the way the shape of the face looks when you try to compare it to the puppet. We saw that with Palisades EB exclusive when Misfit Toy changed her hair. So, the face may not be changed, but it may look likei t was, which pretty much means it was.
matleo is right about comparing Palisades and Sideshow though. For one thing, Palisades egts a chance to redo a character multiple times in the line if they want. Sideshow gets one shot. Unfortunatly with character like Fozzie and Link, they don't seem to spend as much time in the sculpting process as Palisades. And matleo is also right when he says that Palisades has to worry about function when sideshow only needs to worry about form, but that being said, shouldn't all the busts really look fantastic than? A figure really shouldn't look better than a bust. Not trying to knock the busts because they are all pretty cool, but I think sideshow should have spent a little more time on these.
Oh, and after series 6, a great exclusive would be a Jim Henson bust as either puppet or man. THat would complete the collection.