Most ads are bought and sold based on impressions, and the measurement of impressions is done via a 3rd party to ensure the publisher doesn't over-report the am

Most ads are bought and sold based on impressions, and the measurement of impressions is done via a 3rd party to ensure the publisher doesn't over-report the amount of impressions they delivered. Advertisers also typically pay for some level of ad verification to ensure their ads appear on the sites they are targeting, and were in-view when clicked, etc. The model you described works fine for a directly sold placement; the publisher places the ad for a fixed amount of time for a fixed fee. They may still want to have impression and conversion tracking via a 3rd party to measure performance across the multiple sites/ad networks they may be buying on. A pure HTML ad could absolutely work and be ad-block proof, but that doesn't really scale for pubs or advertisers. I have seen that model where the publisher represents a very specific audience, like a trade association. It really doesn't work on a general content site unless there is a high degree of faith from the publisher to the advertiser.