I’ve suggested many times that Microsoft should disable third-party cookies by default in IE10 (and Safari does currently). This would be strategic for them: it devalues Google’s main income source and allows Microsoft to trumpet a commitment to privacy.
This cookie-based approach would functionally prevent user information from going to third parties. (Microsoft has not made any commitment to setting this default.)
Microsoft has, however, chosen a more political path to the same goal, by sending a “Do Not Track” header in IE10.
It’s political because the DNT has no functional value — it does nothing to prevent information from going to third-parties. Instead, it sends a notification to advertisers that the user wishes not to be tracked. The advertiser then makes a choice about whether to comply.
Advertisers — including presumably Google — are upset because this looks like future legal liability. Perhaps a lawsuit is brought, on behalf of a user or a class, saying, “look, I told you not to track me, but you did”.
The DNT header currently has no legal status (AFAIK) and is merely a standard ratified by an industry group. However, the gov’t is supportive.
I understand Microsoft’s political canniness in this, but I hate this sort of regulatory competition. It’s not unlike defensive (or offensive) patents: one company says to another, hey, I’d hate to see an expensive trial for you in the future.
Disabling cookies achieves the goal by competing on product; the DNT header uses legal risk as a weapon.