How do ad blockers affect revenue? Don't they still fetch the ads but just limit the presentation of the ads? So it would be indistinguishable from someone who just does not click on the ads?
2. Even if they did this would be very unreasonable, either you view adverts and the publisher gets paid or you don't view adverts and the publisher doesn't get paid. If you're triggering the pay-out criteria without actually doing whatever is required (view, click, interact) it's just moving the financial hit to the advertiser, which is still unreasonable.
Not my problem. The entire point of HTML is that the server sends files and I have a client that decides how to interpret them. I may be using a browser that is set to display larger fonts for my poor eyesight, or I may be using a mobile browser that decides to use different CSS, or I may be using Lynx that doesn't show images, or I may be using a browser that displays some images and not others based on a blacklist. It's not up to the server to determine.
Only if you own both the site and the ad network otherwise you'll be unable to tell if they made a request for the ad or not. There are also ways of getting false positives with that sort of test, for instance if for whatever reason the server that has the ad on it isn't reachable from the client (say a problem in one of the major backbones, or a bad DNS entry).
The usual approach I've seen sites take is they have some sort of "Please disable your ad-blocker" image that they load everywhere ads go, and then just overlay the ad image on top of that one when it loads.
