Of course legal contracts can contain mistakes, and even intentional fraud. But when that happens, we don't have to just throw our hands up and say "Well, the contract is immutable, so you're screwed unless you happen to be friends with the guy who runs the blockchain."
That's actually exactly what happens in a few of the cases mentioned. In fact, in one of them, the courts chose not to fix the error because it would set a dangerous precedent (which is what you are saying would never happen).
Some contracts are declared void by the judge because they are against the current legislation.
In ethereum the contract is the law (until the people at the top are ok with it, otherwise they will unilaterally change the law)
http://www.duhaime.org/LawFun/LawArticle-151/Famous-Attorney...