By serving up some HTML, you're giving away content - you might have some rules about redistribution, of course, but esentially, you're giving some HTML and/or images to someone's browser to render as they see fit. If they choose to ignore or excise some of it, that's their business. For instance, screen readers for blind people ignore images.

I sympathize with the advertiser's point of view, because I have several sites myself that get a little bit of money from adsense. However, I'm enough of a believer in freedom to think that if people want to block ads more than they want free content, well, that's what the market will give them in some way or another.