"It is our policy not to include attributions of figures and tables" - what does this mean?
While I have not encountered this before, my guess is that the journal has decided to discriminate against non-academic citation (e.g., crediting of image sources per Creative Commons licenses).  

While I believe that this is improper and unethical, I have encountered worse.  I have, in fact, encountered a major journal that refused to allow citation of anything that was not a journal article, because that journal's field does not typically have peer-reviewed conferences.  To somebody coming in from computer science like myself, this is clearly incorrect and unethical: the editors of the journal, on the other hand, saw themselves as manning the barricades in defense of scientific quality and refusing to allow inadequately peer-reviewed material to infiltrate their publication.

In short: I think this is another case of "academia varies more than people think it does," in this case unfortunately being baked into a journal's policy, and would recommend anyone encountering such a policy to simply make their case as suggested by the policy.