Viewership in tv and radio isn&#x27;t measured directly, but indirectly through polls and surveys. You&#x27;re counted as part of the set of potential viewers based on your age, location and whether or not you have a Nielsen box (or whatever they use nowadays.) TV stations don&#x27;t actually <i>know</i> that you decided to turn the channel, and they don&#x27;t really care, since that time has already been paid for.<p>When you can very accurately determine how many people have seen a web ad and you know how many people haven&#x27;t, that more directly affects how much value can be extracted from that advertising. In terms of the actual effect on revenue, blocking a web ad would seem to have more impact than ignoring a tv or radio ad.