I agree MS gave them a good excuse to get out of a system they didn't want to deal with, but it's a reasonable argument that defaulting DNT to on makes it not a user expression of intent. Even one of the Apache devs thought so and submitted a patch to ignore specifically IE10's DNT flag. Although the powers that be eventually rolled that patch back.
In a way, MS poisoned the well, no? Either by (as you state) providing a convenient excuse (possibly intentionally or unintentionally), or by using the flag as a jab at Google. It almost doesn't matter why they did it. The net result was that DNT was ignored by FB, Goog, Apple, Amazon, Adobe and Yahoo -- only Twitter (who use Google Analytics, oddly) went against the grain. MS was warned by a number of marketers this would be the result too, and MS responded with a rather hostile press release.
And yes it's PR... there's PR going around on all sides here -- that's part of what I am saying. Google et. al. are not innocent bystanders here, dont get me wrong, but I am trying to see the whole picture.
I think we'll have to agree to disagree on this one but I am glad that we both seem to want the same end-game: protecting user privacy. As long as there are smart, good people working on this goal, I think it's probably OK that it proceed on several fronts.
Personally I am more concerned about other data aggregators than Google (et. al.) though. If you look at companies like HireRight, Experian (et. al.) -- these companies are truly invading peoples lives. Most of the advertising networks are just selling targeting buckets (e.g. target your ad to males over 45 who make over $150k). But the credit bureaus control people's ability to get a house, to buy a car, to get a job. And there is no way to opt out of that.
Anyways, cheers for the debate.