Do people running Adblock still generate ad revenue?

As you may know, Adblock for Firefox blocks ads from appearing in videos, both on Youtube and Blip and often blocks ads on live streams as well. Would be interesting to know how this affects ad revenue. If ad revenue is not generated, I'd make sure to disable it promptly on any sites I actually care about and want to support, including Day[9] and TL.

I've heard both things here: that the ad serving company can detect whether an ad is actually being played and thus will not generate revenue from people using Adblock and that the site only counts pageviews and ad revenue is based off of that. I suspect it might be different from site to site, aswell.

Anyone know for sure?

Edit: typos.