The minimum requirement for non-functional data is described at [[http://www.gnu.org/philosophy/google-engineering-talk.html#copyright-art-vs-software]] and also at [[http://www.gnu.org/licenses/licenses.html#OtherWorks]], more precisely, the reasoning behind such requirement is better explained at [[http://www.gnu.org/philosophy/google-engineering-talk.html#freedom-2-moral-dilemma]] and also at the section following the previous reference (section 8).
About OpenMW: When I started out as free/libre software activist, I also thought out that things like OpenMW, Wine, QEMU, Mednafen, and so on would be useful *only* for using already-existing non-free software. However, they can also be used to develop other things. I don't have concrete examples, but you *are indeed* right in the regards that we mustn't lock ourselves into using these free/libre software in order to use other non-free software or (as I'm a free/libre software activist) to make use of non-shareable non-functional data.
