On the one hand, you do not have a monopoly over land in the sense of copyright. Sure, you control the use of the particular piece of land, but if someone else wants to copy it by reshaping their own land to have the same topography as yours, you have no recourse. Also, if someone wants to make a derivative work, like a map, they are free to do so. In this sense, the land is in the public domain.
On the other hand, you already have indefinite government granted monopoly of creative works in the sense of land ownership. You can write a novel, print it, bind it, and put it in a drawer. As long as you just have the one copy and don't give it to anyone else, the government will protect your right to exclusive usage and ownership of the work. In this sense, the book is protected property like land.
Where the equivalence falls apart is when you want to sell or transfer the property. If you sell your land, you have no say in what the new owners do with it. If you sell a book, you expect to be able to control what the new owners do with it. This is why this comparison is not very useful.
It's interesting that you bring this up, as in many European countries, moral rights of the author are explicitly separate from copyright:
You can assign copyrights, but not moral rights. I believe that distinction stems from France, but I'm familiar with it from Norway, and variations of it is widespread throughout Europe.
For example, you typically have a legal right to have your name on a work, regardless of copyright. You also typically have a legal right to have your name removed from the work if alterations are made that affects the integrity of it, or that may be detrimental to the creators reputation (e.g. imagine someone deciding to alter key sentences in your political treatise to make it mean the opposite of your original), again irrespective of copyright.
So the protection of a creators moral rights does in Europe explicitly not require a wider interpretation of copyright.
http://en.wikipedia.org/wiki/Natural_law
Animals are territorial and that's really the end of that.
However, the idea of owning an idea ... that's a legal construct and a very recent one at that. The idea of owning an idea would be entirely foreign to someone a thousand years ago.
And the idea that you have a moral claim on owning an idea is just patently absurd, for a very simple reason.
You have no means of proving one way or another that you were the first person to have that very thought. It is entirely possible someone else had it long before you. What claim to ownership can you have? Because you commercialized the idea first?
Most countries are moving to a "first to file" system to simplify bureaucracy, so now your moral claim is contingent not even on your business acumen, but on your ability to quickly fill out a form.
Artists contribute to world culture. George Lucas may own Star Wars in a narrow technical sense (something something disney, I know), but from a cultural standpoint, he can't take it away. It has become part of our culture, part of our written and visual language. A vast amount of energy and derivative art has been spent enjoying and celebrating Star Wars. It has outgrown the original author, because that is what all human artifacts are: derivatives, copies, reinventions, reimaginations.
If copyright were 40 years, Star Wars would be up in 2017. That's more than enough time.
Imagine, if you will, that a "corporation" had existed since ancient times that owned the copyrights on all of the Art, Maths, Literature and other intellectual treasures that have enriched humanity as a whole. Do you really want an immortal, gatekeeper entity that could hold back the entire progress of humanity?
Before you claim that supposition as absurd, consider that we now have at least one company that has "existed" since 705 A.D. (1,309 years ago):
Land is a limited, scarce resource. Ideas are infinitely reproducible, mutable, and changeable.
I can copy your words and you've still got them.
Works of art survive because they are reproduced. This is why still-existing older works are so much better, having been heavily selected already.
Given the already ridiculous difficulty in identifying copyright holders in some cases presently, creating an eternal paperwork burden is a sure way to ensure that works become legally unusable, preventing them from being reproduced and ensuring their demise.
My personal opinion is that copyright should never expire. Think about it: you can have an indefinite government granted monopoly over land, something you didn't create, something that existed before you and will exist after you, but you have weaker protections over something you brought to life? Something that would not exist without you? To me, the moral case for indefinite copyright protection is stronger than the one for indefinite land ownership.