update-debian-edu-artwork is provided by debian-edu-artwork, however there is only a weak Recommends dependency of the subpackages debian-edu-artwork-emerald on the main package whereas the main package has a strong dependency on any of the subpackages.
Adding a Requires on the main package creates a dependency loop which would as far as I understand the policy manual be broken arbitrarily, so it doesn't seem to be a good solution. The most simple fix I can think of would be to copy the script into each subpackage instead of symlinking it, that way we don't have to maintain multiple copies. However I'm wondering why the package is set up the way it is, couldn't we rename debian-edu-artwork to debian-edu-artwork-common, make the theme subpackages require that and turn debian-edu-artwork into a virtual package provided by each theme subpackage? -- Guido Berhoerster