Your views on the law are irrational, but lets apply them to you and see how we get on.
Your models use .nif or are in pcx form, both of which formats were not invented by You nor were you in any way particularly involved (read: not at all) in their creation; you simply use them in some of your creations.
So using your logic your model can be downloaded altered and adapted by someone, without your permission, or credit because the files are standard formats and they put in a lot of "hard work" into them, therefore they belong to them as you have nothing to do with their work.
Perhaps you might argue that what matters is what the data in the file is and to what purpose it is meant to be used for.
And you'd be right to, in law that is the only thing that matters, so you cannot say that your files are not dependent on the game and claim exclusive rights to them.
Once they are used in a mod the license agreement applies which is:
Now we are are prepared to give you this, which is very reasonable of us considering
Modder says that permission is required. Derivative works are only allowed with permission, as long as no other rights are violated.
But this is not reasonable, you have no legal, ethical or moral right to claim this
Modder says that No Derivative works are allowed.
Now you may say the opinion of people like me is worthless but having uploaded files, doesn't make you qualified to express an opinion on the law.
The game manufacturer has chosen to make their Code freely available, no permission required.
A person who has enjoyed the freedom to change at will, the manufactures code cannot then expect to claim exclusive rights and
nor can you claim that they have nothing to do with the game as they are clearly intended for that purpose.
Therefore you cannot refuse permission to others to use your code, without good reason and "they might make a mess of your files" is not a good reason to refuse, 2K let you do what you want with their game without getting precious about it so should you!
It is not a matter of forcing you, it is a question of duty to the modding community.
Modding requires sharing, how else can we mod, if 2K hadn't shared their game your models would be pointless.
Therefore the principle of sharing should be upheld by the modding community
but it is reasonable that we should ask, out of respect for the work you have put in.
But you must have a good reason to refuse to sanction a request, and if you don't have a good reason you should sanction it, out of respect to 2K who have made it possible.
If you can't show some respect , why should we respect you?
Probably my english has become poorer, or your understanding of what i said was peculiar. The fact that i did not invent the pcx or nif does not in any way mean i do not own my work which just happens to be adapted or released in that format.
You then go on to speak of the community, when i, and not you, am the one who shares his works here, and abide by its laws. Namely i accept that i have zero control over what people do in their private modding of my work. However public derivatives are another issue alltogether; why should i be made to "share" my rights there? Just because you say it? Or due to some shadowy good of the community? Most active modders in civIII are artists themselves- due to the old age of the game- many modders of civIV are the same, and to them the request for control over derivatives sounds logical.
As for code used by me (?) i simply make 3d models. I have no use of code of any kind, and certaintly not of 2k's or Firaxis'. Like i said my work is not only used in civ, since it is 3d it is used in other games as well (eg Total War). Now if you were reffering to the code made by the programmers of Blender, then your argument again has been answered: Blender has an agreement with its community that the works of the artists made with Blender do not in any way belong to the Blender corporation; any other stance would have been suicidal for Blender since then no one would want to use it.
You are thinking of this issue in purely computer-game terms, and then purely civ terms, and, lastly, purely CFC ones. What if i were a graphical artist making paintings with 3d software? Would Blender own my work? (then i could not ever sell it to anyone, like painters do). Or would some site own it, lets say DeviantArt, just because i had uploaded it there?
The answer to all that is that simply you missed the point, or altered it for whatever reason. Copyright remains with the original artist, anything else will open a huge can of Cthulic Deepones...