I can imagine advertisers ignoring the DNT header in IE, just because it’s on by default.
Since it’s always on by default, it doesn’t really express the users preference. (Especially since the options menu in IE is one of the worst option screen around, and finding it will most likely be too hard for the average person (even
if they
know that the option exists)
Besides… they (legally spoken) don’t HAVE to respect the header, do they?