Note that there is no question (IANAL, TINLA) that openttd infringes the copyright on Transport Tycoon in any jurisdiction that recognizes the doctrine of "mise en scene", i. e., pretty much any jurisdiction that has a copyright law. See Micro Star v. FormGen.
In general, Debian should not be distributing game clones, in main, in contrib, or anywhere else. The fact that copyright holders rarely bother to pursue legal action against half-assed clones of obsolete games does not mean that they are legitimate in the eyes of the law. Cheers, - Michael