Yes, that is the whole point. Those people who are interested can send the Do Not Track header to indicate the preference. By sending it even when the user didn't indicate that preference, IE would have been the Boy Who Cried Wolf. Network owners wouldn't has been able to trust the header to indicate actual user preference.
I think you are conflating two problems - setting to off by default is also setting a default user preference - that the user wants to be tracked. This may or may not be the case - whether the default is on or off that will be the majority setting since most people don't know / dont't care enough to change it.
I think a couple other posters here have pointed out the larger problem - without ads like this, the free internet dries up and suddenly you need to start paying for everything from gmail to facebook (or whatever other tools/blogs/webcomics any of us visit).
