Cergorach said:
I'm pretty certain that around here (netherlands) contracts can't take away rights granted by the law (there are fare to many stoopid people around that don't read contracts before they sign them).
This is true in the US, as well. A contract that itself violates the law or requires one of its parties to violate the law would not be held up in court.
For example, if I make you sign a contract to work for me for 50 cents an hour, that would be overturned (minimum wage law would overrule it).
Or, if I sign a contract to be enslaved, that wouldn't hold water.
Suppose I get you to sign a contract that says, under certain circumstances, you'll have to hunt down and kill someone. Wish me luck getting a court to enforce that.
On the other hand, there are many rights and privileges that it is perfectly reasonable to sign away (assuming you do so willingly, and you are getting something in return). For example, an NDA curtails your freedom of speech, if you are a playtester: I give you confidential access to a game project in development; in exchange, you agree not to talk about it or tell everyone on the web about it. Should that be nullified because of your right to free speech, which lets you talk about whatever you dang well please?
Employment contracts often include non-compete clauses. A CEO is hired and paid a handsome salary, and the company that hires him doesn't want him to jump ship to a competitor (bringing knowledge and trade secrets with him, perhaps) who offers a bigger salary. Thus the contract says, If you leave voluntarily, or are fired for good reason (e.g., not doing your job, embezzling, etc.), you agree not to work in this industry for X length of time. On the other hand, if we lay you off or fire you for no good reason, you're free to work wherever you want.
The OGL and D20 licenses certainly do make restrictions on publishers. However, they also provide things in return. No one has to agree to the licenses, but if you want to have safe access to certain things, without mucking around in some very gray areas of intellectual property law (areas where people spend big bucks in court sorting out disagreements), the licenses offer a darned good deal.