That's one case but I will give you another one: the Morrowind/Oblivion mods. Even if the same company made both games (Bethesda) and even if they have released modding tools, they stricly forbid porting any assets from one game to another.
I'm not going to discuss the legal aspects of this on the boards for professional reasons but in any event, what other companies do and whether or not people got into legal trouble for this in the past doesn't matter here. Our forum rules are clear: we do not accept mods containing ported assets and we do not tolerate discussions about how to port assets from one game to another. This rule is there to stay and we will make no exceptions.