You have to remember that it's not just about the physical tracking, it's also about time. If the page takes seconds to run it's not feasible on billions of requests because the tracking software sits in between the page getting paid and the target destination. If your tracking script takes seconds (this technique only works after the page is loaded), or provides a white screen jump period, it isn't something that will be desired. Unless of course all other options are removed.

Getting all pages on the web to remove the old image based cookie tracking in support of JS etc... also will never happen unless extreme circumstances occur. Most of the people running ad sites have no idea what you are talking about anyway in realms outside of Cookie and Tracking.