Zazzle responded

[kerravonsen]

This is part of the letter I got in response to my first query (but not my second, they haven't responded to that yet)

Generally speaking, we cannot fulfill any orders containing a copyright or trademark protected title, name, or image. Examples of infringing material include:

--pictures or names of celebrities
--names of characters from books, films, or television shows
--titles of books, feature films, television shows, or magazines
--images from films, television shows, video games, or the internet

So it seems that they are applying their TOS - "pictures or names of celebrities" and "names of characters from books, films or television shows" and "titles of books, feature films, television shows or magazines" - but they are still applying it unfairly and inconsistently.