They're doing something other than checking for ad block extensions. I use a host file and Edge and Forbes tells me to disable my ad blocker. Can't read anything on their site.
Guessing....try to plop down a cookie on your computer from the (blocked) adserver, then check to see if the cookie's there.
I get "disable adblocker" notices on some sites too, even with Adblock disabled, because Ghostery also is there, blocking trackers and their ilk.
:hmm:
So here's a thought:
Google Glass, with eye-tracking technology.
"An ad was displayed, but you did not look at it enough. Please view the following ad, ensuring that your eyes remain focused within the indicated area at all times. Audio output will be unmuted during this time."