There are also pop ups (like the EU cookie warning), self-triggering modals, A/B testing experiences, and newer patterns like feedback widgets that give false positives.

I am working on a visual diff engine that will account for all of these, you can sign up for updates here:

http://geodiff.launchrock.com/

Fair point.

I don't deal with a lot of sites that serve ads, but I do deal with a lot of sites that are on CDNs. Was more my target user group.