Yes that's exactly right. Your post led me to realize that Bulbapedia is storing media in a location outside of /w/, which is why their rules are similar, but images still get crawled. I guess the solution is to move the media somewhere else.
It looks like almost all the other NIWA wikis are doing the same. All except Lylat and Nookipedia. Nookipedia lets crawlers go everywhere, I would assume Lylat does as well.