[lolatu54]

Ads have many specialized requirements that you wouldn't really want to build yourself. Tracking, tokenization of url parameters, rotating ads to meet impression goals, and typically advertisers have build their ads to be served by major ad networks, so you would have to replicate their systems to support those ad units. Ads are way more complicated than most people realize.

[georgeott]

I've heard some Ad networks are asking clients to setup reverse-proxys, so they can make the image APPEAR to come from same origin. It's getting crazy!

[tomtang0514]

As an engineer in a Ads company, I totally agree. It's not just grab ad content from your customer, write some api integration with various publisher and send them the ad. The complexity involved in serving an ad properly and efficiently is way beyond the understanding of outsiders. Rotation, different kind of measurable metrics (we have at least 3x metrics than you can see from google analytics), ad serving efficiency (believe or not, we are able to serve ads faster than some publishers serve their own content), tons of targeting configurations and more. Tracking makes all those things possible.

[blakeyrat]

It's possible the industry could build some sort of "cross advertiser network API" that would allow proper accounting/selection of ads while remaining on one company's domain (from the perspective of that user's web browser). It would require the cooperation of a lot of parties, many of which (optimizing firms for example) have a vested interest in the way things work now.