What about visually overlaying all the ad areas with something else ... lets say whitespace or cat-pictures instead? ;-)
If you just don't want to see ads, by all means overlay them and your ad blocker will probably go undetected.
But a lot of people run ad blockers to save bandwidth or avoid being tracked or to avoid the malware that's been known to be distributed through even the most reputable ad networks. Overlays don't solve those problems.