This is what I used to think, but the diversity of the devices in the developing countries (for example) adds more specifics. Even in countries where there is a lot more homogeneity of devices - you mention HN for example, but if I install ABP on my device and visit multiple sites using the browser, remember that the list of sites is another little trail of breadcrumbs. That could only become significant if the advertisers themselves share this data amongst themselves and combine it with user-agent + geocoded address, but you can count on a service which will pop up to facilitate exactly that (assuming one doesn't already exist). Not to mention, what if these ad networks consolidate at some point in the future?