I honestly don't know if Microsoft in 2011 was doing this for unsurprising business reasons (e.g. as a ploy to hurt Google (AdSense was still all-the-rage), because it's good PR, because they had any genuine concern for their users' privacy, and to do anything to win-back market-share from Chrome and Firefox) - or if it was an intentional move to torpoedo the DNT header by showing how useless it is but only because they implemented it precisely so that it would be useless... but Microsoft wouldn't benefit from user-tracking over the Internet anywhere near as much as Google did/does/would-do.
Plus it’s not as if these companies weren’t willing to assume consent in the absence of the DNT flag. It sounds like a bit of BS to suddenly worry about what consent really means when it goes against their bottom line. I don’t see many hands being wrung about whether the user is meaningfully consenting when they click the easiest and most visible button to dismiss a banner that obscures a quarter of their screen.
Somehow that never bothered sites when the default let them track users.