Why Google Built Incognito Mode | Run Of Network
http://runofnetwork.adzerk.com/general/why-google-built-incognito-mode
The reason that Incognito is such a great feature for Google to build is that over time it will reduce the cookie deletion rate of web browsers.
Why we won’t enable DNT by default | Mozilla Privacy Blog
http://blog.mozilla.com/privacy/2011/11/09/dnt-cannot-be-default
Mozilla’s mission is to give users this choice and control over their browsing experience. We won’t turn on Do Not Track by default because then it would be Mozilla making the choice, not the individual. Since this is a choice for the user to make, we cannot send the signal automatically but will empower them with the tools they need to do it.