You seem like you know what you're talking about so let me ask this: Can a reasonable case by made that the contracts were entered under duress and are therefore not applicable? (Sorry for my poor usage of legal terms here, I am not a lawyer.) Because a lot of people feel like they don't have an option -- it's either feed your family and accept whatever BS the company asks you to sign or remain unemployed and broke. Because if you're getting hired at a sizable company, they're not going to change their contracts just for you. You can try your luck at smaller companies but there's no guarantee.
People just shut up and sign not because they don't care about their rights, only because they feel like they have to agree to these terms to get hired on and thereby provide sustenance to their families.
Can't speak to other states, because I don't practice there, but California law is largely governed in this area by a 2000 case in which one of its courts of appeal held that employment contracts in this setting were "contracts of adhesion" and therefore that an arbitration clause in such a contract might be held to be unconscionable in certain circumstances.
The analysis can get complex but the bottom line is that binding arbitration clauses are not automatically deemed unconscionable and unenforceable - they are only unenforceable if they are unfair. In the 2000 case, the court found the clause to be unfair because it required the employee to submit all claims for wrongful termination to binding arbitration while enabling the employer to take its claims against the employee (e.g., a claim for theft of trade secrets) to court. (see a reprint of the decision here: http://www.lawmemo.com/docs/ca/armendariz.htm) (contains a long and very technical discussion of the entire range of issues affecting whether a binding arbitration clause is or is not enforceable against an employee in California).
In practice, then, employers have adjusted their arbitration clauses to make them fair on the surface so as to make them enforceable, no matter how unfairly they might work in practice. For an updated discussion, here for example is a write-up of a 2009 case in which such a clause was enforced by a California appeals court against an employee: http://www.laboremploymentlawblog.com/arbitration-agreements....
IANAL, but "duress" wouldn't be the applicable legal doctrine in that sort of case. There is a concept known as "unconscionability" or "unconscionable clauses" that is relevant: http://en.wikipedia.org/wiki/Unconscionable.
The common description is that you can't sign away your rights. A clause that says you can't sue your employer at any time for any reason, even after you quit, is obviously not going to fly with a court of law. That's the common idea, but it seems to go a bit further than that.
IANAL, but NO. Duress only applies if they bullied you to sign.
On the other hand, other laws may invalidate that clause. See a lawyer.
Also, before you sign any contract (in Australia, if the contract is written by the other party) you can modify it by just "asking for clarification". If you ask the manager what the fine print means, and they say "nothing", it strikes out the fine print (in theory, but in practice you need to convince the court that this happened). You might want to have some written record, preferable signed by the manager, though.
People just shut up and sign not because they don't care about their rights, only because they feel like they have to agree to these terms to get hired on and thereby provide sustenance to their families.