I recognize that other advertisers may have different goals, such as for large, brand-centric advertising campaigns. I'm not an expert on those so can't offer an informed opinion on any specifics. From a casual observer's point of view, I don't see how they're any worse off than the classic "everyone is wasting half of their ad budget, they just don't know which half" of the print/broadcast era. As you say, at least with online ad networks there can be some indication of where the ads are being shown, allowing a level of independent scrutiny by the advertiser if they wish.
Try looking at it from the publisher's perspective. If their ad network can't detect fraud then of all the money the network brings in an increasing proportion will go to fraudulent publishers. Honest publishers will make less and less money and eventually give up on the ad network.
This does seem to assume that ad networks are the main or only way to support sites that rely on ads for their funding. I'm not sure why we should make that assumption, though.
We're talking about a built-in feature to safely and transparently include ad content from a third party in your own site. It seems possible that advertisers could set up standardised content to work with that feature. Then the kinds of hosts who make enough from advertising to be worth keeping it anyway could either delegate to an advertiser's own server or self-host. Payment could be either a direct transfer or use some new, simpler and more transparent service just to handle that aspect.
