Or if a large portion of the industry decides to voluntarily adopt the standard, to counter the threat of legislation.
A number of large ad networks have already announced support for DNT. Sure, there will always be sites that ignore the header, but there's also a realistic chance that it will give users a meaningful choice about how their behavioral data is used by many of the biggest sites they use most often.
As the CTO of an adserving company, I can confirm that we consider (too) strict legislation a big threat, and as such are more than willing to adopt initiatives like the DNT header.
The good thing about legislation is you can go after those minority of bad guys. That's what happens when businesses call individuals who are on these privacy lists, they are reported to a regulator and the regulator investigates.
Telephone networks are still largely national-based. The idea of individual countries implementing "Do Not Track" legislation is a mess. Do they only enforce it on sites based in their own country? If so, it's useless to users. If they apply it to all countries, it won't work.
Ha! People have been getting around the do not call lists in the UK for years now by dialling in from other countries where our regulatory bodies are powerless. Trying to regulate it on the world wide web would be even harder.
Message from Germany: Doesn't look like that from here. Our politicians are fighting the wrong battles and loosing most of them as well. I haven't seen a single law passed in the last 10 years that actually enhanced privacy in the real world.
As if that would be appropriate or necessary to solve whatever privacy problems we have.
It's the U.S. government trying to take anonymity and privacy away from the Internet; do we want them making weak, unenforceable, irremovable laws on how to implement an HTTP header?
It's a lot harder to detect, and probably harder yet to prove, when they're engaging in illicit tracking.