I understand what is being said about Apache, et al ignoring it because it is a default setting and not explicitly indicative of how a user might feel. However, your response still doesn't explain the impact on consumers. How will defaulting to DNT be detrimental to the people not being tracked?
If anything, organizations and companies ignoring the setting whether it's on by default or not seems like it would have a far more negative affect on the browser's users.
A recent study indicates that cost isn't really an issue. http://mobile.nytimes.com/2012/09/02/your-money/framing-prevents-needed-stimulus-economic-view.xml
You have mail.